ANNE LORENZAT

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Review 2017-2018 - Volume 56

The Current State of Customary International Law with regard to the Use of Chemical Weapons in Non-International Armed Conflicts
ANNE LORENZAT^*
Desk officer, Ministry for Migration, Justice and Consumer Protection of Thuringia (Germany) (BA, MA, LLM)

Table of Contents

Introduction
Theory of Customary International Law

Framework for the Examination of Whether a Rule of Customary International Law Exists

State Practice & Opinio Juris
Particularities regarding Prohibitive Customary Rules & Omission

The ICRC Customary International Humanitarian Law Study & Chemical Weapons

Criticism Regarding the Study

Criticism of a General Kind & Regarding Rule 74 Specifically
Preliminary Conclusions

Analysis of the Current State of Customary International Law concerning the Use of Chemical Weapons in Non-International Armed Conflicts

Incidents of Confirmed Use of Chemical Weapons

Use of Chemical Weapons in Non-International Armed Conflicts
Preliminary Conclusions

Resolutions Issued by UN Organs

UN General Assembly
UN Security Council
Preliminary Conclusions

Multilateral Treaties

International Criminal Law Instruments
International Humanitarian Law Treatiesl
Preliminary Conclusions

Conclusions

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^* This paper was written in personal capacity and does not necessarily represent the views of the author's employer. Back

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[…] the progress of civilization should have the effect of alleviating
as much as possible the calamities of war […]. ¹,

I see no profit in the discussion of degrees of acceptability of war; all is horrific.
The reason for attempting to ban chemical war
is to remove one little piece of horror from the whole mosaic. ²,

I. Introduction

In its report of August 2013, the United Nations Mission to Investigate Allegations of the Use of Chemical Weapons in the Syrian Arab Republic concluded that: “chemical weapons have been used in the ongoing conflict between the parties in the Syrian Arab Republic, also against civilians […] on a relatively large scale […] in the Ghouta area of Damascus”. ³ Fact-finding missions have since established that further incidents of chemical weapons use have taken place within the context of the armed conflict in Syria.

The Syrian Arab Republic is – and has been at the time of any of the verified and alleged uses of chemical weapons in recent years – in a state of non-international armed conflict. ⁴ As other States have become actively involved, the conflict is to be characterized as an internationalized non-international armed conflict. ⁵ Because this paper deals solely with the issue of the use of chemical weapons in non-international armed conflicts, the involvement of States other than Syria (the issue whether the so-called ‘Islamic State’ (ISIL) qualifies as a State shall be left for others to discuss) will be disregarded for the purposes of this issue whenever the armed conflict in Syria is referenced. ⁶

Given this qualification of the aforementioned conflict, none of the relevant multilateral treaties regulating the use of means of warfare such as chemical weapons were applicable in the particular situation of the Ghouta attacks of 2013. The Chemical Weapons Convention (CWC) and the Statute of the International Criminal Court (ICC) were not applicable since Syria was not a party to these treaties at the time. ⁷ While Syria is a party to the Geneva Conventions, the applicable provision of Common Article 3 does not make any reference to means of warfare due to its

¹ Declaration Renouncing the Use, in Time of War, of Explosive Projectiles under 400 Grammes Weight, Saint Petersburg, 4 November 1868. Back
² H. D. Crone, Banning Chemical Weapons (Cambridge, CUP, 1992), p. 90 - written before the Chemical Weapons Convention entered into force in 1997. Back
³ United Nations Mission to Investigate Allegations of the Use of Chemical Weapons in the Syrian Arab Republic, Report on the Alleged Use of Chemical Weapons in the Ghouta Area of Damascus on 21 August 2013, UN Doc. A/68/663–S/2013/735, 13 December 2013, p. 21, § 109. Back
⁴ J. Blake and A. Mahmud, ‘A Legal “Red Line”? Syria and the Use of Chemical Weapons in Civil Conflict’, Vol. 61 UCLA Law Review Discourse 2013, p. 247 and M. Hayashi, ‘Reacting to the Use of Chemical Weapons: Options for Third States’, Vol. 1 Journal on the Use of Force and International Law 2014, p. 85. Back
⁵ Cf. L. Arimatsu and M. Choudhury, ‘The Legal Classification of the Armed Conflicts in Syria, Yemen and Libya’, March 2014, pp. 15–19, https://www.chathamhouse.org , and taking into consideration the developments of the conflict in recent years. The authors found that by Spring/Summer 2011 the violence had reached a level of intensity so as to conclude that the threshold for an armed conflict to be in existence had been reached. See also ICRC, ‘Syria: ICRC and Syrian Arab Red Crescent Maintain Aid Effort Amid Increased Fighting’, 17 July 2012, https://www.icrc.org/eng/resources/documents/update/2012/syria-update-2012-07-17.htm, qualifying the conflict as a non-international armed conflict, and UNSC Res. 2361, 29 June 2017, preambular § 9. Unless indicated otherwise, all URLs cited were last accessed on 14 November 2018. Back
⁶ See, e.g., Amnesty International, ‘Amnesty International Report 2015/2016: The State of the World’s Human Rights’, 2016, pp. 351–353, https://www.amnesty.org/download/Documents/POL1025522016ENGLISH.PDF. Back
⁷ Matters concerning the application of the ICC Statute to incidents relating to non-State parties shall be left aside. Syria only acceded to the CWC in 2013. Back

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minimum standard character. The Protocol for the Prohibition of the Use of Asphyxiating, Poisonous or Other Gases, and of Bacteriological Methods of Warfare (Geneva Gas Protocol), to which Syria is a party, ⁸ applies to international armed conflicts. ⁹

Therefore, the incidents in Syria have given new impetus to the legal debate on the state of customary international law regarding the use of chemical weapons in non-international armed conflicts. This brief analysis has illustrated the desirability of a customary rule prohibiting the use of chemical weapons in non-international conflicts, since even if a State is party to the relevant treaties it may withdraw from them at any given time, rendering the respective treaty inapplicable. ¹⁰

When dealing with customary international law, it is tempting to merely refer to the study published by the ICRC on Customary International Humanitarian Law (ICRC Study). ¹¹ Rule 74 of the Study reads: “The use of chemical weapons is prohibited”. The respective summary clarifies that the rule applies to both international and non-international armed conflicts. At this point, this paper could make its final full stop. However, the Study has been criticized for a number of reasons which will be elaborated on later. For now, suffice it to say that while there is consensus that the use of chemical weapons is prohibited under customary law in international armed conflicts, there are ongoing debates concerning non-international armed conflicts this paper will pick up on. ¹²

This paper shall specifically examine the following question: what is the current state of customary international law regarding the use of chemical weapons in non-international armed conflicts? ¹³ Within the scope of the analysis of the question at hand, conclusions shall be drawn on what the term chemical weapons entails, i.e. the use of which means of warfare in particular are to be considered unlawful (given the wide range of chemical weapons in existence, such as blister, blood, and nerve agents etc.). ¹⁴ The analysis of the state of customary international law comprises an examination of incidents of confirmed use of chemical weapons in non-international armed conflicts in the past century. In addition, relevant resolutions of the UN General Assembly and Security Council as well as relevant multilateral treaties are thoroughly scrutinized since they aggregate the practice of many States and provide sources of condensed practice and expressions of opinio juris. Wherever possible, unilateral State practice is taken into consideration; however, it remains for other, much more extensive publications to look into individual States’ practice and expressions of opinio juris in more depth.

For the purpose of this procedure, based on definitions by Spiers and Crone, chemical weapons or chemical warfare agents shall be defined as chemical substances, whether gaseous, liquid, or solid, which might be employed because of their direct toxic effects on man. Such chemicals must be of high human toxicity in field doses, and, when directed towards people, capable of causing permanent or semi-permanent casualties. Herbicides and riot-control agents shall be excluded from the scope of this paper as they are generally tested to ensure they have no long-term toxic

⁸ ICRC, ‘Treaties, States Parties and Commentaries: Protocol for the Prohibition of the Use of Asphyxiating, Poisonous or Other Gases, and of Bacteriological Methods of Warfare, Geneva, 17 June 1925’, https://ihl-databases.icrc.org/. Back
⁹ “[T]he High Contracting Parties […] agree to be bound as between themselves according to the terms of this declaration.” As the analysis below will show, the understanding regarding the Geneva Gas Protocol seems to have evolved regarding its applicability. Back
¹⁰ See, e.g., developments regarding the ICC Statute in 2016 when several States – within a matter of weeks – announced to withdraw from the Statute. Back
¹¹ J.-M. Henckaerts and L. Doswald-Beck (eds), Customary International Humanitarian Law (New York, CUP, 2005) (ICRC Study). The online version of this publication was used for the preparation of this paper, available at https://www.icrc.org/eng/assets/files/other/customary-international-humanitarian-law-i-icrc-eng.pdf. Back
¹² Blake and Mahmud, supra note 4, p. 257. Back
¹³ For the purposes of this analysis, the concept ‘non-international armed conflict’ is to be understood as outlined in Common Article 3 of the Geneva Conventions. Back
¹⁴ R. E. Langford, Introduction to Weapons of Mass Destruction: Radiological, Chemical, and Biological (Hoboken, Wiley-Interscience, 2004), pp. 225–234. Back

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effect on humans (although riot-control agents can be very toxic to humans in the short term, they have little to no effect in the long term), whereas the warfare agents are chosen for the opposite reason of having extreme human toxicity. ¹⁵

The article is divided into five chapters. After this introduction a brief overview of the theory of customary international law is given. A further chapter is dedicated to the ICRC Customary International Law Study and how it plays into this article. The most extensive chapter analyses the current state of customary international law regarding the use of chemical weapons in non-international armed conflicts before conclusions are drawn on the results of the analysis.

II. Theory of Customary International Law

The approach chosen for this paper is to conduct an inquiry into whether a rule of customary international law prohibiting the use of chemical weapons in non-international armed conflicts is currently in existence or not by applying the traditional approach of establishing whether sufficient State practice and respective opinio juris exist. Furthermore, conclusions shall be drawn on the scope of the prohibitive rule in question.

1. Framework for the Examination of Whether a Rule of Customary International Law Exists

A. State Practice & Opinio Juris

The traditional approach towards customary international law is reflected in Article 38(1) lit. b of the Statute of the ICJ: “international custom, as evidence of a general practice accepted as law” is a source of law the ICJ may apply to decide on the disputes brought before it. The elements required for the formation of custom are a sufficient amount of State practice which: “should have been accompanied by, or be backed by, evidence of what is traditionally called opinio juris”. ¹⁶

It is assumed that the readers of this article are familiar with the general theory of customary international law. Therefore, this section will touch upon general matters of establishing whether a customary rule exists and particular matters specific to the research question at hand only in a brief manner, and mention a few particularities regarding the establishment of prohibitive customary rules.

Both verbal and physical acts are considered to constitute State practice (e.g. diplomatic and policy statements, military manuals, comments by governments on draft treaties, pieces of legislation, statements in international organizations and resolutions these bodies adopt count as forms of speech-act ¹⁷). ¹⁸

¹⁵ Cf. E. M. Spiers, A History of Chemical and Biological Weapons (London, Reaktion Books, 2010), p. 11) and Crone, supra note 2, pp. 4, 41–42. The definition used in the paper is based on combined ideas taken from these two sources. Back
¹⁶ H. Thirlway, The Sources of International Law (Oxford, OUP, 2014), pp. 56–57. See also ICJ, Continental Shelf Case (Libyan Arab Jamahiriya v. Malta) , 3 June 1985, I.C.J. Rep. 1985, pp. 28–29, § 27 and International Law Commission (ILC), Report on the Work of the Sixty-Eighth Session, UN Doc. A/71/10, 19 August 2016, ch. V, draft conclusions 2, 3. Back
¹⁷ Continental Shelf Case, supra note 16, § 4; M. E. Villiger, Customary International Law and Treaties: A Manual on the Theory and Practice of the Interrelation of Sources (The Hague, Kluwer Law International, 1997, 2nd ed), pp. 19–23; K. Wolfke, Custom in Present International Law (Dordrecht, Martinus Nijhoff Publishers, 1993, 2nd ed) p. 42 and M. Scharf, ‘Accelerated Formation of Customary International Law’, Vol. 20 No. 2 ILSA Journal of International and Comparative Law 2014, p. 312. Back
¹⁸ A number of legal scholars reject the idea that verbal practice shall count as State practice, since making a certain statement is far from being the same as actually acting in a certain manner. The Report of the International Law Association (ILA) Committee on the Formation of Customary International Law, however, makes a good point in emphasizing that in some cases this may be so, however, “this goes more to the weight to be attributed to the conduct rather than to any inherent ability of verbal acts to contribute to the formation of customary rules”: ILA, London Conference (2000), Committee on Formation of Customary (General) International Law, ‘Final Report of the Committee: Statement of Principles Applicable to the Formation of General Customary International Law, 2000, §§ 3–4, http://www.ila-hq.org/index.php/committees?committeeID=22 (ILA Report). The Permanent Court of International Justice (PCIJ) and the ICJ have treated verbal acts as State practice, too: see, e.g., PCIJ, The Case of the S.S. “Lotus” (France v. Turkey) , 7 September 1927, P.C.I.J. 1927 Ser. A No. 10, pp. 23, 28–30; ICJ, Legality of the Threat or Use of Nuclear Weapons (Advisory Opinion) , 8 July 1996, I.C.J. Rep. 1996, pp. 259–261, §§ 86, 88. Back

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The practice of both executive and legislative organs of a State are usually considered as State practice. ¹⁹ The decisions of international courts and tribunals are not State practice due to their independent nature. According to findings of the ILC, decisions of domestic courts may constitute State practice as well as proof of opinio juris. ²⁰

Regarding the question of how State practice is to be qualified, the North Sea Continental Shelf cases are very instructive: “State practice, including that of States whose interests are specially affected, should have been both extensive and virtually uniform […]”. ²¹ Regarding the required density of practice, the ICJ in the Nicaragua judgment concluded that:

[i]t is not to be expected that in the practice of States the application of the rules in question should have been perfect […] the Court deems it sufficient that the conduct of States should, in general, be consistent with such rules, and that instances of State conduct inconsistent with a given rule should generally have been treated as breaches of that rule […]. ²²

Opinio juris is defined as:

A belief, on the part of the generality of States, that a practice satisfying the criteria [regarding State practice] is sufficient to prove the existence of a rule of customary international law; but it is not […] necessary to the formation of such a rule to demonstrate that such a belief exists, either generally or on the part of any particular State. ²³

It needs to be established that State practice is accompanied by the conviction that such practice reflects a legal obligation. ²⁴ However: “it is logically impossible for [States] to have an opinio juris in the literal and traditional sense, that is, a belief that the practice is already legally permissible or obligatory”. ²⁵

B. Particularities regarding Prohibitive Customary Rules & Omission

It is more difficult to establish a prohibitive rule regarding a certain weapon by relying on omission, since this can be explained in a number of different ways: a State may be convinced that its use would be unlawful; it may lack the resources to acquire such a weapon or necessity to use it; or a State may refrain from its employment for political, tactical or other non-legal reasons. ²⁶ In the Nuclear Weapons Advisory Opinion the ICJ was reluctant to uphold the claim that non-use over a 50-year period supports opinio juris, since it is not manifestly attributable to a belief in the unlawfulness of their usage (“ambiguous omission” ²⁷ ). ²⁸

With regard to prohibitive customary rules it must be considered that – due to the nature of the actions at issue – no large amount of operative practice will be generated. Therefore, the requirements regarding density of practice need to be adjusted accordingly. ²⁹ None of those three

¹⁹ ILA Report, supra note 18, § 9; ILC Report, supra note 16, draft conclusion 6. Back
²⁰ ILC Report, supra note 16, draft conclusions 6, 10. Back
²¹ ICJ, North Sea Continental Shelf Cases (Federal Republic of Germany v. Denmark; Federal Republic of Germany v. Netherlands) , 20 February 1969, I.C.J. Rep. 1969, p. 43, § 74 (emphasis added). Back
²² ICJ, Case Concerning Military and Paramilitary Activities In and Against Nicaragua (Nicaragua v. United States) , 27 June 1986, I.C.J. Rep. 1986, p. 98, § 186 (emphasis added). Back
²³ ILA Report, supra note 18, § 16. Back
²⁴ R. Kolb, ‘Selected Problems in the Theory of Customary International Law’, Vol. 50 No. 2 Netherlands International Law Review 2003, p. 120 and ILC Report, supra note 16, draft conclusion 9. Back
²⁵ ILA Report, supra note 18, § 16. Back
²⁶ W. H. Parks, ‘The ICRC Customary International Law Study: A Preliminary Assessment’, Vol. 99 American Society of International Law Proceedings 2005, p. 210 and A. Thomas and A. J. Thomas, Legal Limits on the Use of Chemical and Biological Weapons (Dallas, Southern Methodist University Press, 1970), p. 157. Back
²⁷ Nuclear Weapons Advisory Opinion, supra note 18, p. 254, § 67. Back
²⁸ Thirlway, supra note 16, p. 61. Back
²⁹ Cf. Kolb, supra note 24, p. 134. Back

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elements (duration, uniformity, generality) are to be seen in isolation, as weaknesses in one element might be overcome by the relatively higher strength of the other elements. ³⁰

With respect to rules of International Humanitarian Law (IHL) the International Criminal Tribunal for the Former Yugoslavia (ICTY) concluded that, because battlefield behaviour is difficult to actually observe, reliance must primarily be placed on elements of verbal practice. ³¹ This caveat will be important for the analysis at hand as it is even more relevant for the establishment of a prohibitive rule.

Therefore, opinio juris is slightly more crucial when trying to establish whether customary law rules of this type exist, since practice will often enough be hard to come by. This means resorting to a negative approach on customary law as it focuses on abstention rather than practice. ³² Under the appropriate circumstances, omissions can count as a form of State practice, when a lack of action is not too ambiguous to draw conclusions from it. ³³

III. The ICRC Customary International Humanitarian Law Study & Chemical Weapons

The ICRC Study’s authors, like the author of the present paper, have applied the traditional method to identify rules of customary law: establishing State practice and whether there is a belief among States that such practice is either required, prohibited, or allowed (depending on the nature of the rule) as a matter of law. ³⁴

Chapter 24 of the ICRC Study covers ‘Chemical Weapons’ and contains rule 74 stating that: “The use of chemical weapons is prohibited.” According to the respective summary: “State practice establishes this as a norm of customary international law applicable in both international and non-international armed conflicts.” ³⁵ As has been hinted at above, though, matters are complicated by certain caveats of the Study.

1. Criticism Regarding the Study

This sub-section focuses on some of the main issues regarding the Study that have incurred criticism. Both general criticism as well as criticism specific to the rule relating to the use of chemical weapons will be mentioned in order to explain why this article is worth reading until the end.

A. Criticism of a General Kind & Regarding Rule 74 Specifically

The extensive ICRC Study has drawn general criticism regarding a few major issues which will be touched on briefly in this sub-section.

The Study has been criticized for progressively developing customary humanitarian law rather than establishing which rules have actually come into existence. The Study’s authors are criticized for reaching far-fetched conclusions at times, for oversimplifying the concept of international custom and adopting tendentious positions. ³⁶ Turns even goes as far as saying that it might be problematic that:

³⁰ Id. , p. 133. Back
³¹ ICTY, Appeals Chamber, Prosecutor v. Dusko Tadić, IT-94-1-A, Decision on the Defence Motion for Interlocutory Appeal on Jurisdiction, 2 October 1995, § 99. Back
³² Thomas and Thomas, supra note 26, p. 136. Back
³³ Akehurst, ‘Custom as a source of international law’, Vol. 47 British Yearbook of International Law 1976, p. 26 and ILA Report, supra note 18, § 6, making reference to the PCIJ’s Lotus Case. Back
³⁴ I. Scobbie, ‘The Approach to Customary International Law in the Study’, in E. Wilmshurst and S. Breau (eds.), Perspectives on the ICRC Study on Customary International Law (Cambridge, CUP, 2007), p. 24. Back
³⁵ ICRC Study, supra note 11, Vol. I, p. 259. Back
³⁶ C. Emanuelli, ‘Comments on the ICRC Study on Customary International Law’, Vol. 44 Canadian Yearbook of International Law 2005, p. 440; W. Boothby, ‘Differences in the Law of Weaponry When Applied to Non-International Armed Conflicts’, in K. Watkin and A. J. Norris (eds.), Non-International Armed Conflicts in the Twenty-First Century (Newport, Naval War College Press, 2012), p. 204 and D. Turns, ‘Weapons in the ICRC Study on Customary International Law’, Vol. 11 No. 2 J.C.S.L. 2006, p. 202. Back

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“the motivation behind the Study is that of securing greater compliance with International Humanitarian Law […] In order to secure greater compliance, it has been felt necessary to develop customary law as far as possible to ‘plug the gaps’ in the corpus of existing humanitarian law”. ³⁷

Authors have generally criticized that for some or even many rules the referenced State practice is insufficiently dense to meet the standard of extensive and virtually uniform practice required for a customary rule to come into existence. ³⁸

Furthermore, the Study has been criticized for its extensive reliance on verbal practice rather than actual deeds. ³⁹ In the same vein, authors have criticized the Study for the normative weight given to some of the materials such as military manuals, which may be influenced by other factors such as political and operational issues rather than legal ones, ⁴⁰ and non-binding UNGA resolutions to which States may lend their support: “for reasons having nothing to do with a belief that the proposition in it reflects customary international law”. ⁴¹

When it comes to weapons, the authors have often referred primarily to the relevant weapons conventions, which in some cases are relatively recent instruments. Haines raises the question of the extent to which customary law based on such recent treaties could have developed within such a short period of time. ⁴²

Methodologically, the authors of the ICRC Study are criticized for the manner in which they tend to assume that prohibitions of particular weapons applicable to international armed conflicts will also be applicable to non-international armed conflicts. ⁴³ They refer to the Tadić Appeals Chamber decision where the ICTY concluded that: “[w]hat is inhumane and consequently proscribed in international wars cannot but be inhumane and inadmissible in civil strife”. ⁴⁴

Haines criticizes the conclusion that prohibitive rules regarding weapons are always equally applicable to both types of conflicts, as such an assumption is not satisfactory when evidence of State practice is of either insufficient quantity or quality to dispense with the distinction. ⁴⁵

In the decision mentioned just now, the ICTY also points out that there are limitations to the applicability of rules governing international armed conflicts to non-international armed conflicts:

(i) only a number of rules and principles governing international armed conflicts have gradually been extended to apply to internal conflicts; and

(ii) this extension has not taken place in the form of a full and mechanical transplant of those rules to internal conflicts; rather, the general essence of those rules, and not the detailed regulation they may contain, has become applicable to internal conflicts. ⁴⁶

To merely transfer a rule established for international to non-international conflicts without proper justification is difficult to accept when the basis chosen for the analysis is the two-element approach demanding proper evidence for the establishment of the existence of a certain rule. The Appeals Chamber in Hadzihasanović had it best when it pointed out that:

³⁷ Turns, supra note 36, p. 235. Cf. Parks, supra note 26, pp. 210–212. Back
³⁸ J. Bellinger and W. Haynes, ‘A US Government Response to the International Committee of the Red Cross Study Customary International Law’, Vol. 89 No. 866 I.R.R.C. 2007, pp. 444–445. Back
³⁹ Parks, supra note 26, p. 210 and Scobbie, supra note 34, p. 25. Back
⁴⁰ Scobbie, supra note 34, p. 38 and Bellinger and Haynes, supra note 38, p. 445. Back
⁴¹ Bellinger and Haynes, supra note 38, p. 445. Back
⁴² S. Haines, ‘Weapons, Means and Methods of Warfare’, in Wilmshurst and Breau, supra note 34, p. 262. Back
⁴³ Turns, supra note 36, p. 210 and Haines, supra note 42, p. 262. Back
⁴⁴ Prosecutor v. Tadić, supra note 31, § 119. Back
⁴⁵ Haines, supra note 42, p. 263. Back
⁴⁶ Prosecutor v. Tadić, supra note 31, § 126. Back

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[T]he Appeals Chamber is aware that it is incorrect to assume that, under customary international law, all the rules applicable to an international armed conflict automatically apply to an internal armed conflict. More particularly, it appreciates that to hold that a principle was part of customary international law, it has to be satisfied that State practice recognized the principle on the basis of supporting opinio juris. ⁴⁷

Some of the most important sources of IHL – most noticeably the Geneva Conventions and their Additional Protocols – are, up until today, based on a strict separation between those rules applicable to international and non-international armed conflicts. Even with respect to more recent treaties such as the ICC Statute, States have held on to this distinction.

Hence, caution is in order when establishing whether rules governing international armed conflicts may be applicable to non-international armed conflicts by virtue of the development of custom.

Rule 74 concerning chemical weapons has been questioned for certain specific reasons which shall be explored at this point.

Rule 74 does not provide a definition of what constitutes a chemical weapon, nor does the respective explanatory chapter name the chemical agents whose use is supposed to be prohibited. The scope of this rule remains unclear.

Some of the data listed in support of the potential rule whose existence is examined here is rather opaque – in a way that makes it difficult to draw any conclusions from it regarding the research question. To name one example: “In 1980, a State denounced and condemned as a war crime the use by another State of chemical weapons during an armed conflict”. ⁴⁸ The respective State is not named, nor is the specific incident or the agent used. Therefore, conclusions regarding the existence of a customary rule cannot effectively be drawn.

The general issue concerning the mere extension of customary rules existing for international to non-international armed conflicts without providing proper evidence or justifying the extension of the rule in a comprehensible manner is equally relevant for rule 74.

B. Preliminary Conclusions

Even though the foregoing analysis shows that the Study is slightly flawed in some regards, it goes without saying that it has been welcomed with a lot of praise ⁴⁹ and is an important instrument in the theory and practice of IHL, having added important insights on customary law to the legal sphere. Without meaning to discredit the Study, for the purpose of this paper, it is necessary to focus on the issues that are being criticized and to take the respective lessons into account. Considering the specific difficulties regarding the credible establishment of the existence of a prohibitive rule in the context of means of warfare, and the re-emergence of the use of chemical weapons in the past few years, the subject of rule 74 deserves being revisited.

This is a good instant to forestall some potential criticism regarding this paper. Certainly, there has been a development toward the convergence of rules applying to international and non-international armed conflicts which the Tadić Appeals Chamber has pointed out as mentioned above. ⁵⁰ The Appeals Chamber, in the same decision, claimed that: “there undisputedly emerged a general consensus in the international community on the principle that the use of [chemical] weapons is also prohibited in internal armed conflicts.” ⁵¹ While this may turn out to be true, it is hardly an obvious result of the analysis the Chamber undertook in merely five paragraphs. Even if a less strict approach was taken toward the question whether a customary rule exists, one would

⁴⁷ ICTY, Appeals Chamber, Prosecutor v. Hadzihasanović & Kubura, IT-01-47-AR72, Decision on Interlocutory Appeal Challenging Jurisdiction in Relation to Command Responsibility, 16 July 2003, § 12. Back
⁴⁸ ICRC Study, supra note 11, Vol. II, ch. 24, § 444. Back
⁴⁹ See, e.g., M. Bothe, ‘Customary International Humanitarian Law: Some Reflections on the ICRC Study’, Vol. 8 Y.I.H.L. 2005, pp. 143–187 and D. Fleck, ‘International Accountability for Violations of the Ius in Bello: The Impact of the ICRC Study on Customary International Law’, Vol. 11 No. 2 J.C.S.L. 2006, pp. 179–199. Back
⁵⁰ Prosecutor v. Tadić, supra note 31, § 119. Back
⁵¹ Id. , § 124. Back

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have to conclude that what the ICTY is presenting as proof of a customary rule cannot be considered as being sufficient.

IV. Analysis of the Current State of Customary International Law concerning the Use of Chemical Weapons in Non-International Armed Conflicts

In this section, available evidence of State practice and opinio juris shall be examined to draw conclusions with regard to the research question at hand. Incidents of the use of chemical weapons, resolutions issued by major UN organs and multilateral treaties will be examined.

1. Incidents of Confirmed Use of Chemical Weapons

Since this paper criticizes the ICRC Study for not taking actual incidents of chemical weapons’ employment and States’ reactions to such incidents into consideration properly, the following section will examine confirmed instances of the use of chemical weapons in non-international armed conflicts.

An integral part of the analysis is the examination of reactions of the international community to chemical weapons use, of which UNGA and UNSC resolutions form a major part. The ICJ has established that the former:

[…] can, in certain circumstances, provide evidence important for establishing the existence of a rule or the emergence of an opinio juris. To establish whether this is true of a given General Assembly resolution, it is necessary to look at its content and the conditions of its adoption [and] to see whether an opinio juris exists as to its normative character. ⁵²

The individual circumstances of the adoption need to be examined on a case-by-case basis, ⁵³ since a vote in favour of a resolution does not necessarily reflect a State’s legal conviction. ⁵⁴ However, under respective circumstances, States voting in favour of a resolution are able to provide the subjective element to the formation process, while the resolution provides indirect evidence of States’ attitudes. ⁵⁵

A. Use of Chemical Weapons in Non-International Armed Conflicts

i. Iraq (1988)

Before the still-ongoing conflict in Syria witnessed its first chemical attack, there had only been one documented instance when chemical weapons had been used in non-international armed conflicts since the beginning of the 20th century. ⁵⁶

⁵² Nuclear Weapons Advisory Opinion, supra note 18, pp. 254–255, § 70 (emphasis in original). Back
⁵³ ILA Report, supra note 18, § 29. Back
⁵⁴ Emanuelli, supra note 36, p. 446. Back
⁵⁵ ILA Report, supra note 18, §§ 30–31 and B. D. Lepard, Customary International Law: A New Theory and Practical Applications (Cambridge, CUP, 2010), p. 180. Back
⁵⁶ Another major – albeit merely domestic – incident took place in 2002 when a group of armed Chechens took around 800 people as hostages at the Dubrovka Theatre in Moscow. During the so-called ‘Moscow Hostage Crisis’ Russian federal security forces eventually released gas into the theatre’s air conditioning system. Of the remaining hostages about 125 died from gas poisoning and hundreds of people were treated for effects of gas exposure; 33 hostage-takers died. The gas employed contained fentanyl components (opioids) which are commonly used as narcotics and anaesthetics. However, this incident did not take place in the context of an armed conflict, even though a link can be established between the hostage-taking incident and Chechnya’s ongoing struggle for independence. The operation carried out by Russian security forces qualifies as a law-enforcement operation (see N. Quénivet, ‘The Moscow Hostage Crisis in the Light of the Armed Conflict in Chechnya’, Vol. 4 Y.I.H.L. 2001, pp. 348–372 for differing opinion): A. Dolnik and R. Pilch, ‘The Moscow Theater Hostage Crisis: The Perpetrators, their Tactics, and the Russian Response’, Vol. 8 No. 3 International Negotiation 2003, pp. 581–585; J. R. Riches et al. , ‘Analysis of Clothing and Urine from Moscow Theater Siege Casualties Reveals Carfentanil and Remifentanil Use’, Vol. 36 No. 9 Journal of Analytical Toxicology 2012, pp. 647–655; ECtHR, Finogenov and others v. Russia, Appl. Nos. 18299/03 and 27311/03, 20 December 2011, Judgment. Back

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In March 1988, chemical weapons were used in the city of Halabja in Northern Iraq. The employment of chemical weapons (mustard gas and different nerve agents) by Iraqi forces took place in the context of the Iran-Iraq War, after the city had been taken over by pro-Iranian Kurdish forces. About 5.000 people – mostly civilians – were killed during and immediately after exposure to these agents. ⁵⁷

It is being assumed that the attacks against the Kurdish population took place due to their continuous struggle for autonomy. ⁵⁸ While the incident occurred within the general context of an international armed conflict, the attack was directed against Iraq’s own population which is why the incident is to be classified as a non-international armed conflict situation. ⁵⁹

In May 1988, the UN Security Council unanimously “condemn[ed] vigorously the continued use of chemical weapons in the conflict between the Islamic Republic of Iran and Iraq contrary to the obligations under the Geneva Prococol”; ⁶⁰ an invocation repeated with almost the same words in a resolution of August 1988. ⁶¹

The wording of the resolution, which was adopted unanimously, ⁶² is strong. The minutes of the session in which the Council voted on the resolution do not contain any information on a debate which may have taken place on its content. ⁶³ Therefore, it is not clear whether the Council considered the use of chemical weapons by Iraq against Iraqi Kurds as an act of warfare within a non-international armed conflict situation. The text of the resolution focuses on the inter-State context and the fact that the Geneva Protocol, an instrument applicable in armed conflict between States (although nowadays often referred to in the non-international context), is referred to explicitly makes it difficult to draw definitive conclusions concerning the research question. The expression of the conviction of the States involved that the use of chemical weapons under the circumstances was in violation of a legal obligation is clear though (“[e]xpects both sides to refrain from the future use of chemical weapons in accordance with their obligations under the Geneva Protocol”, third operative paragraph of UNSC Res. 612).

ii. Syria - Ghouta area

The United Nations Mission to Investigate Allegations of the Use of Chemical Weapons in the Syrian Arab Republic concluded that sarin had been used in the conflict between the parties in Syria on a large scale, including against civilians, in the Ghouta area in 2013. ⁶⁴

In September 2013, the UNSC unanimously ⁶⁵ adopted a resolution concerning this incident, determining: “that the use of chemical weapons anywhere constitutes a threat to international peace and security”. ⁶⁶ It:

⁵⁷ Human Rights Watch, ‘Whatever Happened to the Iraqi Kurds?’, 1991, https://www.hrw.org/reports/1991/IRAQ913.htm . See also BBC News, ‘1988: Thousands Die in Halabja Gas Attack’, 16 March 1988, http://news.bbc.co.uk/onthisday/hi/dates/stories/march/16/newsid_4304000/4304853.stm ; BBC News, ‘Iraqi Kurds mark 25 Years since Halabja Gas Attack’, 16 March 2013, http://www.bbc.com/news/world-middle-east-21814734. Back
⁵⁸ ‘1988: Thousands Die in Halabja Gas Attack’, supra note 57. Back
⁵⁹ Also characterizing the Halabja incident as part of a non-international armed conflict: L. Tabassi, ‘Impact of the CWC: Progressive Development of Customary International Law and Evolution of the Customary Norm Against Chemical Weapons’, 63 The CBW Conventions Bulletin 2004, p. 3. Back
⁶⁰ UNSC Res. 612, 9 May 1988, §§ 2, 3. Back
⁶¹ UNSC Res. 620, 26 August 1988, § 1. Back
⁶² UNSC Res. 620, 26 August 1988. Back
⁶³ UNSC Official Records, 43rd year, 2825th meeting, UN Doc. S/PV/2825, 26 August 1988. Back
⁶⁴ Report on the Alleged Use of Chemical Weapons in the Ghouta Area of Damascus on 21 August 2013, supra note 3, p. 8. Back
⁶⁵ UNSC Official Records, 68th year, 7038th meeting, UN Doc. S/PV.7038, 27 September 2013, p. 2. Back
⁶⁶ UNSC Res. 2118, 27 September 2013, § 1. Back

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[c]ondemn [ed] in the strongest terms any use of chemical weapons in the Syrian Arab Republic [and]
[d] ecide [d] that the Syrian Arab Republic shall not use, develop, produce, otherwise acquire, stockpile or retain chemical weapons, or transfer, directly or indirectly, chemical weapons to other States or non-State actors. ⁶⁷

The resolution also refers to the Geneva Protocol (in recalling that Syria acceded to the Protocol in 1968). ⁶⁸ This UNSC resolution gives an insight into how the Geneva Protocol is perceived today. Even though the conflict in Syria is a non-international one, the Council still referred to the Protocol, which was originally designed to apply to international conflicts only. The resolution was adopted unanimously ⁶⁹ despite its very strong wording and reference to the particular and far-reaching wording of the Chemical Weapons Conventions’ Article I, §§ 1 lit. a and b.

In its resolution of January 2014, the UNGA “[s] trongly condemn [ed] the use of chemical weapons in the Syrian Arab Republic, which is prohibited under international law, amounts to a serious crime and has a devastating impact on civilians”. ⁷⁰ The wording, again, is very strong. In addition to condemning the use of chemical weapons, a very general reference is made to such use being prohibited under international law. The resolution was adopted by 127 votes to 13 with 47 abstentions. ⁷¹ It is rather surprising that this UNGA resolution drafted in response to an actual incident of chemical weapons employment was adopted with a number of negative votes and abstentions. The reasons given for negative votes and abstentions are the “politicized” resolution, its “selective” and “punitive” approach and reasons of non-intervention. ⁷² It is important to note, however, that the states voting in favour of the resolution represent all Regional Groups of the United Nations, including chemical weapons possessor states.

These resolutions can be qualified as acts of verbal state practice. Regarding those states voting in favour of the respective resolutions, opinio juris as to the prohibition of the use of chemical weapons – also with regard to non-international armed conflict scenarios – is incorporated in this act. Cases of voting against such a resolution or abstaining during the vote, conviction as to the opposite effect, may be shown.

iii. Syria - Incidents Investigated by the Joint Investigative Mechanism (JIM)

In the following sub-section, incidents of alleged use of chemical weapons in Syria that have been investigated by the JIM will be discussed. Thereby, the alleged use by Syrian Arab Armed Forces and ISIL will be examined separately.

A fact-finding mission, established under Security Council resolution 2235 (2015), created and conducted by the Organization for the Prohibition of Chemical Weapons (OPCW), had concluded: “with a high degree of confidence that chlorine has been used as a weapon […] in the villages of Talmenes, Al Tamanah, and Kafr Zita” in Syria. ⁷³ Chlorine is a lung agent which irritates the eyes and throat and, when used in high concentrations, inflames the lung tissues, leading to pulmonary oedema, accumulation of fluid in the lungs and eventually death from lack of oxygen. ⁷⁴ Of the 350 to 500 reported casualties of these attacks, 13 died. ⁷⁵

⁶⁷ Id. , §§ 2, 4. Back
⁶⁸ Id., preambular § 4. Back
⁶⁹ UNSC Meetings Coverage, Security Council Requires Scheduled Destruction of Syria’s Chemical Weapons, Unanimously Adopting Resolution 2118 (2013) , UN Doc. SC/11135, 27 September 2013. Back
⁷⁰ UNGA Res. 68/182, 18 December 2013, § 1. Back
⁷¹ UNGA Res. 68/PV.70, 18 December 2014, pp. 25–26. Back
⁷² UNSC Meetings Coverage, General Assembly Adopts 68 Resolutions, 7 Decisions as It Takes Action on Reports of Its Third Committee, UN Doc. GA/11475, 18 December 2013. Back
⁷³ OPCW, Note by the Technical Secretariat: Third Report of the OPCW Fact-Finding Mission in Syria, UN Doc. S/1230/2014, 18 December 2014, § 3 (Third JIM Report). When assessing the results of the report, one needs to keep in mind certain aspects of the respective investigations. For instance, the investigation was, in some cases, carried out more than two years after the incident and sources of information and material were often of secondary or tertiary nature (see § 29 of the report). However, given the very careful approach and wording of its findings, valuable conclusions can be drawn from the report. Back
⁷⁴ Spiers, supra note 15, pp. 14–15 and A. Kelle, Prohibiting Chemical & Biological Weapons. Multilateral Regimes and Their Evolution (Boulder, Lynne Rienner Publishers, 2014), pp. 25–26. Back
⁷⁵ Third JIM Report, supra note 73, Annex 2, § 1.8. Back

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In Talmenes, two attacks with toxic chemicals were established to have taken place in April 2014. The fact-finding mission found evidence of five incidents in April and May 2014 in Al Tamanah and of 17 attacks between April and August 2014 in Kafr Zita. ⁷⁶ According to the information available on these three villages, none of them was under the control of the Syrian Arab Republic at the time of the incidents. ⁷⁷ The JIM, ⁷⁸ in its third report, later found sufficient information to conclude that incidents involving the use of toxic substances in the following locations were caused by Syrian Arab Armed Forces: Talmenes (April 2014) and Sarmin (March 2015). ⁷⁹ Regarding an incident in Qmenas in March 2015 the JIM determined that a Syrian Arab Armed Forces helicopter had dropped one device or barrel bomb in Qmenas: “Although the Leadership Panel was close to having sufficient information to reach a conclusion on the actors involved, at the current stage it could not draw a conclusion with certainty as to whether the device or barrel bomb contained explosives or chlorine”. ⁸⁰

A Security Council resolution was drafted in reaction to the incidents in Talmenes, Sarmin and Marea and the respective JIM findings. ⁸¹ Reaffirming that the use of chemical weapons constitutes a serious violation of international law and recalling the determination of the Security Council to identify those parties responsible for the use of any chemical weapons in the Syrian Arab Republic, the 42 States sponsoring the draft resolution were determined to act under Chapter VII of the UN Charter, taking measures under Article 41. ⁸² The actions they suggested included the compilation of a list of individuals and entities who (among other things) were responsible for, engaged in or otherwise involved in the use, transfer, acquisition, proliferation, development, manufacture or production of chemical weapons in the Syrian Arab Republic. ⁸³ Among other things, the member States were supposed to freeze all funds, other financial assets and economic resources in their territories at the date of adoption of this resolution or any time thereafter, which were owned or controlled by the individuals and entities on the list; they would have also been obliged to take the necessary measures to prevent the entry into or transit through their territories

⁷⁶ Third JIM Report, supra note 73, Annex 2, §§ 5.6, 5.30, 5.59. Back
⁷⁷ Id., §§ 5.2, 5.28, 5.54. Back
⁷⁸ The JIM was established based on UNSC Res. 2235, 7 August 2015 (adopted unanimously, see: UNSC Meetings Coverage, Security Council Unanimously Adopts Resolution 2235 (2015), Establishing Mechanism to Identify Perpetrators Using Chemical Weapons in Syria, UN Doc. SC/12001, 7 August 2015). Its mandate entails: “to identify to the greatest extent feasible individuals, entities, groups, or governments who were perpetrators, organizers, sponsors or otherwise involved in the use of chemicals as weapons […] in the Syrian Arab Republic where the OPCW FFM [fact-finding missions] determines or has determined that a specific incident in the Syrian Arab Republic involved or likely involved the use of chemicals as weapons, including chlorine or any other toxic chemical”. The JIM is to work in coordination with the OPCW FFM to fulfil its mandate (§§ 5, 9). The FFM is not mandated to reach conclusions about attributing responsibility for chemical weapons use (cf. preambular § 8), hence the need for a measure like the JIM. Back
⁷⁹ Third JIM Report, supra note 73, p. 13, §§ 54–56. Back
⁸⁰ Id. , pp. 15–16, §§ 64–65. In January 2017, Reuters published information linking the inner circle of President Assad and senior military personnel of the Syrian Arab Republic to the incidents investigated by the JIM. The news site explains how the JIM had previously only identified military units responsible for the attacks in question, and how, later on, a list – seen by Reuters journalists, who have not been able to independently review the results of the inquiry – has been produced, naming 15 individuals whom investigators have linked to a series of chlorine bomb attacks in 2014 and 2015. The people listed include Syria’s President Assad, his brother (commander of an elite armed forces division), the defence minister and the head of military intelligence. Furthermore, the air force chief, four commanders of air force divisions and a number of other senior military personnel were included in the list. A former commander of British and NATO divisions interpreted the list as reflecting the military chain of command. According to him, if a chemical attack was planned and executed, one would expect these individuals to be included in the process. The information indicates that the decision to use toxic weapons came from the very top and was then delegated down for execution. As of yet, the list has not been published officially, nor has further information been made available: A. Deutsch, ‘Exclusive: Assad Linked to Syrian Chemical Attacks for First Time’, Reuters, 14 January 2017, http://www.reuters.com/. Back
⁸¹ UNSC Draft Res. S/2017/172, 28 February 2017. Back
⁸² Id. , preambular §§ 3, 4, 16. The 42 States sponsoring the resolution represented the Western European and Others Group (WEOG) and Asia-Pacific Group of the UN General Assembly members. Back
⁸³ Id. , § 15 lit. a. Back

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of the listed individuals if the resolution had been adopted. ⁸⁴ The draft resolution, in its annex, was already equipped with said list. In addition, the resolution was supposed to establish a Committee of the Security Council to, for example, monitor the implementation of the measures imposed in the draft resolution and designate individuals, groups and entities to be subject to the measures imposed by the resolution and consider requests for exemptions in accordance with the resolution. ⁸⁵ 3 Security Council members voted against the resolution (China, Russia, Bolivia) and 3 abstained (Egypt, Ethiopia, Kazakhstan). ⁸⁶ The reason for the resolution not being adopted by the Council is most likely that it entailed such far-reaching demands toward member States as well as the significant competences the envisioned committee was supposed to have. Russia officially based its veto on the fact that it questioned the methods and findings of the JIM which the draft resolution’s sponsors acted upon. ⁸⁷ The representative of Bolivia reiterated: “its strongest and most absolute condemnation and rejection of the use of chemical weapons […] regardless of who uses them or the reasons for doing so or where such acts are perpetrated”. Bolivia justified its negative vote, among others, by referring to the fact that the annexed lists had not been compiled by the experts of the JIM. ⁸⁸ China’s representative also stressed that his country: “oppose[s] the use of chemical weapons by any State, organization or individual under any circumstances, and call[s] for punishing all instances of chemical weapons use”. China’s veto was explained by the existing differences among Security Council members regarding the facts of the chemical weapons incidents in question. ⁸⁹ Taking the vetoing States by their words, one has to conclude that their vetoing the draft had nothing to do with a differing opinio juris regarding the use of chemical weapons but rather certain specific aspects of the draft resolution. Also, the fact that a large number of UN members sponsored a strongly worded and far-reaching draft resolution shows how serious a high number of States are about punishing and preventing the use of chemical weapons.

Concerning two incidents in Kafr Zita in April 2014 the JIM Leadership Panel:

determined that the Syrian Arab Armed Forces had executed air strikes in that area on that day. However, the Panel could not confirm the use of barrel bombs because the remnants of the device allegedly used had been removed and could not […] be linked with certainty to [any of the impact locations]. ⁹⁰

Another incident took place in Khan Shaykhun (Idlib Governate) in April 2017. Based on findings by the OPCW Fact-Finding Mission, ⁹¹ which had concluded that a large number of people, some of whom died, had been exposed to a chemical weapon, the JIM conducted an investigation. The Leadership Panel was confident that the Syrian Arab Republic was responsible for the release of sarin at Khan Shaykhun on 4 April 2017. ⁹²

A draft resolution “[c]ondemn[ing] in the strongest terms the reported use of chemical weapons” ⁹³ in Khan Shaykhun in April 2017 was vetoed by Russia and was met with a negative vote by Bolivia, while China, Ethiopia and Kazakhstan abstained. ⁹⁴ The draft referred to the use of

⁸⁴ Id. , §§ 17, 21. Back
⁸⁵ Id. , § 13 lit. a, c. Back
⁸⁶ UNSC Official Records, 72nd year, 7893rd meeting, UN Doc. S/PV.7893, 28 February 2017, p. 4. Back
⁸⁷ Id. , pp. 6–7. Back
⁸⁸ Id. , pp. 10–11. Back
⁸⁹ Id. , pp. 9–10. Back
⁹⁰ Third JIM Report, supra note 73, pp. 15, 17, §§ 61–63, 71–74. Back
⁹¹ UNSC, Letter dated 18 May 2017 from the Secretary-General addressed to the President of the Security Council, UN Doc. S/2017/440, 19 May 2017. Back
⁹² UNSC, Letter dated 26 October 2017 from the Leadership Panel of the Organisation for the Prohibition of Chemical Weapons-United Nations Joint Investigative Mechanism addressed to the Secretary-General (Enclosure: Seventh Report of the Organisation for the Prohibition of Chemical Weapons-United Nations Joint Investigative Mechanism) , UN Doc. S/2017/904, 26 October 2017, pp. 7–10 (Seventh JIM Report). Back
⁹³ UNSC Draft Res. S/2017/315, 12 April 2017, § 1. Back
⁹⁴ UNSC Official Records, 72nd year, 7922nd meeting, UN Doc. S/PV.7922, 12 April 2017. Back

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chemical weapons as: “constitut[ing] a serious violation of international law”. ⁹⁵ Had it been adopted, it would have allowed for:

immediate and unfettered access to individuals whom the OPCW or the United Nations, including the JIM, [had] grounds to believe to be of importance for the purpose of the mandate, and specifically […] the obligation upon the Syrian Arab Republic to provide the JIM and FFM with the following and take the following steps: […] flight plans, flight logs, and any other information on air operations; […] names of all individuals in command of any aircraft. ⁹⁶

It was only six months after the vote on this failed resolution that the JIM published its findings regarding the likely perpetrator; however, the draft already pointed to the Syrian Government as the likely source of the attacks. Russia based its opposition to the document on its prejudging character regarding the outcome of an investigation that was yet to come; Bolivia followed with a similar argument. ⁹⁷ None of those vetoing or abstaining verbalized a change in legal opinion regarding the use of chemical weapons; criticism regarding the draft was rather based on political and procedural matters. The fact that an attempt at renegotiating the draft was made strongly suggests that all the States involved were interested in achieving the adoption of a resolution that would have condemned the chemical weapons incident at issue.

The US carried out missile strikes on the air base in Syria from which the chemical attack on Khan Shaykhun was supposedly launched. ⁹⁸ The strikes were a direct response to the chemical weapons attack, as was confirmed by the US Government. ⁹⁹ A US defence official said that the strikes which hit aircrafts, fuel storage, weapons dumps and other equipment were aimed at: “send[ing] a message to the Syrian regime that any use of chemical weapons would not be tolerated”. ¹⁰⁰ The President of the United States himself presented the official reasons for the strikes:

Tonight, I ordered a targeted military attack on the air field in Syria from where the chemical attack [at Khan Shaykhun] was launched […] It is in this vital national security of the United States to prevent and deter the spread and use of deadly chemical weapons. ¹⁰¹

The lawfulness of the US air strikes will not be discussed further in this paper. However, legal scholars are rather unanimous regarding its unlawfulness. ¹⁰² What is important for the matter at hand is that the US, with documented verbal support after the fact by the UK, Australia, Israel, Saudi Arabia and a certain sympathy from Italy and Japan, ¹⁰³ apparently felt so strongly about the (at that point alleged) use of chemical weapons by Syrian Government forces that it felt compelled to act by unlawful military means. This shows strong support of the unlawfulness of chemical weapons use under international law. ¹⁰⁴

⁹⁵ UNSC Draft Res. S/2017/315, supra note 93, preambular § 2. Back
⁹⁶ Id. , § 5. Back
⁹⁷ S/PV.7922, supra note 94, pp. 7, 9 respectively. Back
⁹⁸ E. McKirdy, J. Hanna and B. Starr, ‘Syria Strikes: Site of Chemical Attack Hit Again’, CNN, 9 April 2017, http://edition.cnn.com/2017/04/08/middleeast/syria-strikes-russia-donald-trump/index.html and M. R. Gordon, H. Cooper and M. D. Shear, ‘Dozens of U.S. Missiles Hit Air Base in Syria’, The New York Times, https://www.nytimes.com/2017/04/06/world/middleeast/us-said-to-weigh-military-responses-to-syrian-chemical-attack.html. Back
⁹⁹ B. Starr and J. Diamond, ‘Trump Launches Military Strike Against Syria’, CNN, 7 April 2017, http://edition.cnn.com/2017/04/06/politics/donald-trump-syria-military/index.html. Back
¹⁰⁰ McKirdy, Hanna and Starr, supra note 98. Back
¹⁰¹ Starr and Diamond, supra note 99. Back
¹⁰² See, e.g., M. Milanovic, ‘The Clearly Illegal US Missile Strike in Syria’, EJIL: Talk! , 7 April 2017, https://www.ejiltalk.org/the-clearly-illegal-us-missile-strike-in-syria/ and H. P. Aust and M. Payandeh, ‘Praxis und Protest im Völkerrecht: Erosionserscheinungen des völkerrechtlichen Gewaltverbots und die Verantwortung der Bundesrepublik im Syrien-Konflikt‘, Vol. 73 No. 13 Juristen Zeitung 2018, p. 640. Back
¹⁰³ A. Yuhas, N. Lhomami, J. Grierson and C. Phipps, ‘US says Russia Bears Responsibility for Assad’s Gas Attack – As It Happened’, The Guardian, 8 April 2017, https://www.theguardian.com/world/live/2017/apr/07/us-syria-response-donald-trump-assad-pentagon-live. Back
¹⁰⁴ The same holds true for France’s – so far just verbal – reaction to an alleged chlorine attack carried out by Syrian Government forces in early February. France’s President Macron told the press that France would: “strike the place where these launches are made or where they are organized”. See BBC News, ‘Syria War: “Chlorine Attack” on Rebel-Held Idlib Town’, 5 February 2018, http://www.bbc.com/news/world-middle-east-42944033 ; BBC News, ‘France’s Macron Threatens Syria Strikes if Chemical Weapon Use Proven’, 14 February 2018, http://www.bbc.com/news/world-europe-43053617 and M. Pennetier and M. Rose, ‘“France Will Strike” if Proven Chemical Bombs Used in Syria: Macron’, Reuters, 14 Feburary 2018, https://www.reuters.com/article/us-mideast-crisis-syria-france/france-will-strike-if-proven-chemical-bombs-used-in-syria-macron-idUSKCN1FX2PT. Back

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In April 2018 the US, France and the UK launched more than 100 missiles against Syria in reaction to a chemical weapons attack in Douma, allegedly committed by Syrian Government forces. ¹⁰⁵ While again, scholars have qualified the attacks of the Western allies as being unlawful, ¹⁰⁶ and several States such as Russia, Iran and China denounced the strikes by the US, France and the UK, other Western allies such as the German Government referred to them as “necessary and proportionate”. ¹⁰⁷ As mentioned before, while two wrongs do not make a right, the fact that States are willing to break the rules of international law themselves in reaction to a breach points to a strong position regarding the unlawfulness of chemical weapons use. It may even be assumed that the missile strikes were conducted so as to avoid “failure to react over time to a practice”, ¹⁰⁸ even though, admittedly, failure to react in this particular scenario could not overwrite rules of written international law.

The repetitive employment of chemical weapons by Syrian Government forces since Syria’s accession to the Chemical Weapons Convention shows disregard for its treaty obligations under the Convention. It constitutes elements of State practice. However, it is difficult to determine an actual lack of opinio juris. No party will deny that there is a legal obligation under the Convention to not employ chemical weapons. It is also difficult to assess this matter for the time before Syria acceded to the Convention. Furthermore, Syria does not qualify as a persistent objector to the kind of rule whose existence this paper is analysing. The State has become a party to the Convention after all, and rather than denying a rule or obligation, the Syrian Government continuously denies the use of the weapons in question – including for the time before it acceded to the Chemical Weapons Convention. ¹⁰⁹

In May 2014, a draft Security Council resolution aiming at referring the situation in Syria to the International Criminal Court, among others, because of the use of chemical weapons, was blocked by two vetoes. ¹¹⁰ There was no precedence for the JIM, being a non-judicial investigative mechanism, undertaking an investigation into the identification of perpetrators, organizers, sponsors or those otherwise involved in the use of chemicals as weapons. ¹¹¹ One may think of the JIM as a form of a (temporary) substitute for judicial proceedings aimed at bringing those responsible for chemical weapons attacks to justice, in that it collects and evaluates evidence regarding alleged chemical weapons use and perpetrators. This underlines that the fifteen States which adopted the resolution, representing all Regional Groups of the UN system, believe in the

¹⁰⁵ J. Borger and P. Beaumont, ‘Syria: US, UK and France Launch Strikes in Response to Chemical Attack’, The Guardian, 14 April 2018, https://www.theguardian.com/world/2018/apr/14/syria-air-strikes-us-uk-and-france-launch-attack-on-assad-regime and BBC News, ‘Syria Air Strikes: US and Allies Attack “Chemical Weapons Sites”’, 14 April 2018, https://www.bbc.com/news/world-middle-east-43762251. Back
¹⁰⁶ See, e.g., M. Milanovic, ‘The Syria Strikes: Still Clearly Illegal’, EJIL: Talk! , 15 April 2018, https://www.ejiltalk.org/the-syria-strikes-still-clearly-illegal/ and Aust and Payandeh, supra note 103, p. 633. Back
¹⁰⁷ Press Release of the Federal German Government, ‘Bundeskanzlerin Merkel zu den Militärschlägen der USA, Großbritanniens und Frankreichs in Syrien', 14 April 2018, https://www.bundesregierung.de/Content/DE/Pressemitteilungen/BPA/2018/04/2018-04-14-syrien.html. Back
¹⁰⁸ ILC Report, supra note 16, draft conclusion 10, § 3. Back
¹⁰⁹ In an interview published as late as April 2017, Syria’s President Assad claimed that his country had never used its chemical arsenal in its history and that it had given up its chemical weapons three years earlier: BBC News, ‘Assad Denies Use of Chemical Weapons’, 13 April 2017, https://www.bbc.com/news/av/world-middle-east-39586500/assad-denies-use-of-chemical-weapons. Back
¹¹⁰ UNSC Meetings Coverage, Referral of Syria to International Criminal Court Fails as Negative Votes Prevent Security Council from Adopting Draft Resolution, UN Doc. SC/11407, 22 May 2014. Back
¹¹¹ Third JIM Report, supra note 73, p. 7, § 18. Back

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prohibition of the use of such means of warfare under international law and want to see it enforced. ¹¹²

In a later resolution triggered by further allegations that chlorine had been used in Syria since early 2015 ¹¹³ the UN Security Council: “[c]ondemn [ed] in the strongest terms any use of any toxic chemical, such as chlorine, as a weapon in the Syrian Arab Republic”. ¹¹⁴ The resolution refers to the use of chlorine without assigning responsibility for it to any party of the conflict. ¹¹⁵ It was adopted with 14 votes in favour, 0 against, and 1 abstention. Venezuela justified its abstention by saying that the vote prejudged the results of the then-ongoing OPCW investigation. ¹¹⁶ Noting that there was no vote against the resolution, and assuming that the reason verbalized by the representative of Venezuela was the actual reason keeping it from concurring with the majority of UNSC members, the resolution was very strongly backed. It is also strongly worded. Again, the resolution serves a twin role: a vote in favour constitutes an act of State practice, which incorporates a reflection of opinio juris.

iv. Syria - Alleged Use of Chemical Weapons by ISIL

In 2015, ISIL reportedly launched several chemical attacks using chlorine and mustard agents in Syria, for example in Marea in the Aleppo Governorate. ¹¹⁷ Eventually, the JIM found: “sufficient information to conclude that Islamic State in Iraq and the Levant (ISIL) was the only entity with the ability, capability, motive and means to use sulphur mustard in Marea on 21 August 2015.” ¹¹⁸

By means of resolution 2209 the Security Council had already “[c]ondemn[ed] in the strongest terms any use of any toxic chemical, such as chlorine, as a weapon in the Syrian Arab Republic” and, utilizing the language of the Chemical Weapons Convention: “[r]eiterate[d] that no party in Syria should use, develop, produce, acquire, stockpile, retain, or transfer chemical weapons”. ¹¹⁹

The resolution was triggered by an OPCW Fact-Finding Mission report which had concluded with a high degree of confidence that toxic chemicals had been used as a weapon. ¹²⁰ The attribution of responsibility for the reported incidents was not part of the mandate of the mission, ¹²¹ which is most likely what explains the phrasing of the fourth preambular paragraph, which refers to: “no party in Syria”.

The resolution is also instructive in that it does not differentiate between State and non-State actors. Without referring to either party of the conflict, the use of any toxic chemical, such as chlorine, is condemned in the strongest terms. The Security Council uses very strong language and further adds that: “those responsible for any use of chemicals as weapons, including chlorine or any other toxic chemical, must be held accountable”. ¹²² The conviction that even for entities which are not party to any relevant treaty, the use of chemical weapons shall be considered unlawful or at least illegitimate, may be considered as reference to a respective prohibitive rule of customary international law.

¹¹² See preambular § 4 of UNSC Res. 2235, supra note 78, making reference, generally, to a “serious violation of international law” next to several specific references to the CWC, to which Syria was already a party at the time. Back
¹¹³ UNSC Res. 2209, 6 March 2015, preambular § 6. Back
¹¹⁴ Id. , preambular § 1. Back
¹¹⁵ Id. , preambular § 7. Back
¹¹⁶ UNSC Meetings Coverage, Adopting Resolution 2209 (2015), Security Council Condemns Use of Chlorine Gas as Weapon in Syria, UN Doc. SC/11810, 6 March 2015. Back
¹¹⁷ Amnesty International, supra note 6, p. 352 and Human Rights Watch, ‘Syria: New Deadly Chemical Attacks – Strong Security Council Action Needed’, 28 September 2016, https://www.hrw.org/news/2016/09/28/syria-new-deadly-chemical-attacks. Back
¹¹⁸ Third JIM Report, supra note 73, § 58. Back
¹¹⁹ UNSC Res. 2209, supra note 113, preambular §§ 1, 4 (emphasis added). Back
¹²⁰ Cf. id. , § 2. Back
¹²¹ Third JIM Report, supra note 73, § 4. Back
¹²² UNSC Res. 2209, supra note 113, preambular § 6. Back

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It also needs to be noted that the resolution was adopted with 14 votes in favour and 1 abstention (Venezuela), making it a resolution with strong support by UNSC member States. The resolution has been discussed more in detail in the above section on the JIM-investigated incidents. For the reasons mentioned above, the abstention shall not be regarded as impeding the strong condemnation expressed towards the use of chemical weapons in general and toxic chemicals in particular. ¹²³

Based on the conclusions of a 2017 OPCW Fact-Finding Mission report ¹²⁴ the JIM investigated incidents of 15 and 16 September 2016 in Umm Hawsh (Aleppo Governate) which involved two casualties. The JIM concluded that sulphur mustard was delivered via mortar shell. The Leadership Panel was confident that ISIL was responsible for the incidents. ¹²⁵

As has been mentioned above, findings by the OPCW Fact-Finding Mission have triggered a more thorough investigation by the JIM with its further-reaching mandate that includes the competence to determine which entity is responsible for chemical weapons attacks.

The fact that the JIM with its extensive mandate was established ¹²⁶ (based on a joint action by the US and the Russian Federation) at all makes a strong case for the common opinio juris and consequent practice of member States regarding the use of chemical weapons as being an unlawful act under international law. The renewal of the mandate by means of Security Council resolutions 2314 of 31 October 2016 and 2319 of 17 November 2016, both of which were adopted unanimously, ¹²⁷ shows that the States involved were committed to giving the JIM the opportunity to actually find out who was responsible for the attacks under investigation to make a case against impunity.

However, when the mandate was due to be renewed the respective draft resolution ¹²⁸ proposing renewal for one year sponsored by 41 States was vetoed by Russia, Bolivia voted against, while China and Kazakhstan abstained in October 2017. ¹²⁹ Both Russia and Bolivia criticized the timing of the vote on the draft resolution since the next JIM report was due only days later. They argued in favour of reviewing the report and then deciding on the need to further extend the JIM’s mandate. ¹³⁰ Russia furthermore criticized the methodology applied by the JIM, as did Egypt, a State that voted in favour of the draft resolution. ¹³¹ The Russian Federation did not imply that it had in any way changed its legal opinion on the use of chemical weapons, ¹³² while Bolivia clearly condemned the use of chemical substances as weapons which the State considers to be a serious

violation of international law and international peace and security. ¹³³ The abstaining China and Kazakhstan also stressed that they were opposed to the use of chemical weapons under any

¹²³ UNSC Meetings Coverage, supra note 116. Back
¹²⁴ UNSC, Letter dated 4 May 2017 from the Secretary-General addressed to the President of the Security Council, UN Doc. S/2017/400, 5 May 2017. Back
¹²⁵ Seventh JIM Report, supra note 93, pp. 7–9. Back
¹²⁶ See details on the JIM, supra note 80. Back
¹²⁷ UNSC Meetings Coverage, Security Council Unanimously Adopts Resolution 2314 (2016), Extends Mandate of Joint Investigative Mechanism to Identify Perpetrators of Chemical Weapons Use in Syria, UN Doc. SC/12571, 31 October 2016 and UNSC Meetings Coverage, Unanimously Adopting Resolution 2319 (2016), Security Council Extends Mandate of Mechanism to Identify Perpetrators Using Chemical Weapons in Syria, UN Doc. SC/12594, 17 November 2016. Back
¹²⁸ UNSC Draft Res. S/2017/884, 24 October 2017. Back
¹²⁹ UNSC Official Records, 72nd year, 8073rd year, UN Doc. S/PV.8073, p. 7. Back
¹³⁰ Id. , pp. 2–4. Back
¹³¹ Id. , pp. 5, 17 respectively. Back
¹³² In a letter to the Secretary-General, the Permanent Representative of the Russian Federation reiterated that “all Council members firmly condemn the use of chemical weapons wherever and by whomsoever and believe that those responsible should be identified and held to account” and stressed that the issues for Russia related in fact to the methodology of the JIM: UNGA, Letter dated 6 October 2017 from the Permanent Representative of the Russian Federation to the United Nations addressed to the Secretary-General, UN Doc. A/72/526-S/2017/848, 10 October 2017. Back
¹³³ Id. , p. 10. Back

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circumstances by anyone and that in their opinion, the JIM should continue its work. What both these countries opposed was the timing of the vote on the draft resolution as well as the political circumstances of its creation. ¹³⁴

In November 2017, three further attempts regarding the renewal of the JIM’s mandate were made. On 2 November, the US and Russia circulated competing draft resolutions regarding the matter. The US draft characterized the information obtained by the JIM as constituting “sufficient, credible and reliable evidence to reach conclusions on those responsible for the use of chemical weapons”, while the Russian text expressed its methodological concerns. Russia stressed its opposition to the methodology and continued to refuse engaging on the US draft. The US opposed the inclusion of language deriving from the Russian draft which might have been considered to discredit the previous work of the JIM and the independence and professionalism of its staff. On 16 November, both drafts were voted on; neither of them was adopted. The US draft was vetoed by Russia; the Russian draft received only four votes in favour (Bolivia, China, Kazakhstan and Russia). After that, Japan circulated a draft which would have extended the JIM’s mandate for one month while requesting the UN Secretary-General and the OPCW to submit proposals to the Council for the structure and methodology of the JIM which was to reflect views of Security Council members. Twelve members voted in favour of the draft resolution on 17 November, which was eventually vetoed by Russia. ¹³⁵

Members of the Security Council made further attempts to find a compromise before the expiration of the JIM’s mandate. Italy circulated a draft letter to the Secretary-General requesting for the JIM’s organisational and administrative arrangements to be maintained until 31 December 2017 pending a final decision on the renewal of its mandate. Furthermore, Sweden and Uruguay circulated a draft resolution to extend the JIM’s mandate for a year, adding language regarding the methodology of the JIM. Eventually, Russia opposed both of those initiatives. The lack of an adopted resolution resulted in the end of the JIM’s mandate. ¹³⁶

The number of attempts to ensure the continuation of the JIM’s investigative work and the statements referred to above must lead the observer to the conclusion that while the Council failed to agree on a resolution to that effect, it does not reflect a changed opinio juris or even practice regarding the use of chemical weapons. It shows a deep political division between members of the Security Council which, while strongly disagreeing on a number of issues such as how the JIM shall conduct its work and how its conclusions need to be interpreted, still agreed on the necessity of such a body to provide for those responsible for the use of chemical weapons to be held accountable.

B. Preliminary Conclusions

In recent years, a whole new body of physical State practice regarding the use of chemical weapons in non-international armed conflicts has developed. The particularity of prohibitive customary rules does not allow for definite conclusions based on non-existing acts of State practice in the shape of non-use. However, while the recurring employment of such weapons in Syria sends a strong signal with regard to that particular State’s stance toward chemical weapons use, the international community has, as has been shown above, made its conviction as to the prohibition of the use of such means of warfare abundantly clear as well. The disregard of Syrian State authorities for rules of international law – since Syria has acceded to the Chemical Weapons Convention in 2013, the employment of chemical weapons violates treaty law, irrespective of the existence of a customary rule whose existence has yet to be proven – hast not been left uncommented by the international community. The latter has taken a number of actions in order

¹³⁴ Id. , pp. 13, 15–16. Back
¹³⁵ Security Council Report, ‘In Hindsight: The Demise of the JIM’, January 2018, http://www.securitycouncilreport.org/monthly-forecast/2018-01/in_hindsight_the_demise_of_the_jim.php?print=true. Back
¹³⁶ Id. Back

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to not let the acts described call a (customary) prohibitive rule regarding chemical weapons into question.

Some may hold that the use of chemical weapons in the instances described above risks undermining a potentially existing norm proscribing the use of chemical weapons and may legitimize such use for the future. ¹³⁷ Others may argue that the fact chemical weapons are used at all could also mean that no such norm exists. The employment of chemical agents as means of warfare constitutes acts of physical State practice. However, whenever chemical weapons were used in the context of an armed conflict, the international community usually reacted unequivocally with verbal acts strongly condemning such employment and even more so in recent decades. Furthermore, whenever the Syrian Government was alleged or proven to have employed chemical weapons, it denied doing so. Even though proof has been delivered by fact-finding missions contradicting those statements, they are being upheld and repeated. Therefore, one may assume that the Syrian Government is indeed aware of its legal obligation – whichever source it may stem from – not to engage in the use of chemical weapons.

The reactions to the incidents in non-international armed conflicts were clear in condemning the use of chemical weapons in the strongest terms. None of the relevant resolutions explicitly referred to customary law, but often to the Geneva Protocol. A UNSC resolution following a particular incident in Syria referred to the Geneva Protocol despite the fact that this treaty was originally only applicable to international armed conflicts. ¹³⁸ This can be interpreted as hinting to a common belief by States that the content of the Protocol has crystallized into a customary norm applicable to non-international armed conflicts as well. This matter will be elaborated on further at a later stage.

The degree of consent to UN General Assembly and UN Security Council resolutions regarding (alleged) incidents of chemical weapons use has fluctuated. While an UNGA resolution in reaction to the Ghouta incident being verified by a UN mission saw 47 abstentions, ¹³⁹ we have seen a UNSC resolution adopted unanimously on the same matter which did not only condemn the use of sarin, but went very far in mandating that Syria was not to acquire in any way or use chemical weapons. However, whenever chemical weapons have been allegedly used in recent times, the international community has come together to condemn such acts, thereby expressing their majority opinio juris concerning the respective means of warfare.

2. Resolutions Issued by UN Organs

In this section, resolutions adopted by the UN General Assembly and Security Council concerning chemical weapons shall be examined. The ILC mentions “resolutions adopted by an international organization or at an international conference” specifically as forms of State practice, ¹⁴⁰ which: “may provide evidence for establishing the existence and content of a rule of customary international law, or contribute to its development”. ¹⁴¹ Resolutions that have already been mentioned in the above sections are disregarded at this point. ¹⁴² Rather than referring to specific instances of chemical weapons use, the UN documents analysed in this section generally bear a more general relation toward chemical weapons.

The legally binding character of UNSC resolutions makes them generally more likely to influence States’ behaviour. But then again, there can only be a maximum of 15 for those adopted from 1966 on (11 votes in favour of resolutions ratified before 1966). Such resolutions, though binding,

¹³⁷ C. Jefferson, ‘Origins of the Norm against Chemical Weapons’, Vol. 90 No. 3 International Affairs 2014, p. 660. Back
¹³⁸ See the wording of the Protocol for the Prohibition of the Use of Asphyxiating, Poisonous or Other Gases, and of Bacteriological Methods of Warfare, Geneva, 17 June 1925: “[…] Contracting Parties […] to be bound as between themselves according to the terms of this declaration.” Back
¹³⁹ UNGA Res. 68/182, supra note 70. Back
¹⁴⁰ ILC Report, supra note 16, draft conclusion 6. Back
¹⁴¹ Id. , draft conclusion 12, § 2. See also Scharf, supra note 17, p. 313. Back
¹⁴² Where voting results are not mentioned in the footnotes, they have not been found. Resolutions that have already been considered in conjunction with the analysis of a specific incident will not be mentioned again in the current section. Back

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are by nature less representative than UNGA resolutions. At the same time, there may be General Assembly resolutions – which, if they are not internal ones are not legally binding – but contain highly persuasive and compelling language and have a high number of approving votes. Therefore, they may have just as much influence on States’ behaviour or represent States’ opinion on the matter more to the point as a legally binding UNSC resolution, possibly more. As was mentioned above, UNGA und UNSC resolutions are considered to be an expression of opinio juris of the States involved.

The resolutions mentioned hereafter do not necessarily refer specifically to non-international armed conflicts. However, as they may provide valuable insight into the attitude States have taken towards chemical weapons over time on a more general note, they are analysed as well. While the ICRC Study lists resolutions in relation to the use of chemical weapons ¹⁴³ the following section takes a closer analytical look at specific resolutions.

A. UN General Assembly

The relevant UNGA resolutions taken into account have been categorized according to the approach taken towards the matter.

i. Chemical Weapons as Weapons of Mass Destruction as Danger/Threat or General Call for Disarmament regarding Weapons of Mass Destruction

In a number of resolutions, the UNGA took a slightly different approach by “[c]onsidering that weapons of mass destruction constitute a danger to all mankind and are incompatible with the accepted norms of civilization”, then calling on States to accede to the Geneva Protocol and observe the relevant obligations. ¹⁴⁴ In another resolution the UNGA stated that it was: “[d]etermined, for the sake of all mankind, to exclude completely the possibility of the use of chemical weapons”. ¹⁴⁵

The wording of these resolutions is rather strong. It remains unclear what is meant by an incompatibility with accepted norms of civilization. One might read general principles of international humanitarian law into this, for example the prohibition to cause unnecessary suffering or to use weapons which are indiscriminate by nature. This could imply that States voting in favour of the resolution opine that these weapons are already unlawful under customary law. The resolution employing this particular wording was adopted in 1968, with 91 votes in favour (of 126 member States at the time). ¹⁴⁶ On the other hand, calling on norms of civilization and expressing determination to exclude the possibility of the use of certain means of warfare might as well be hinting at the fact that there was no general confidence towards the existence of an actual legal obligation to renounce the use of the weapons at issue. What is clearly expressed, though, is a general conviction that the use of chemical weapons shall be unlawful under international law.

¹⁴³ ICRC, ‘Customary IHL: Practice Relating to Rule 74. Chemical Weapons’, https://ihl-databases.icrc.org/customary-ihl/eng/docs/v2_rul_rule74. Back
¹⁴⁴ UNGA Res. 2162 (XXI) B, 17 November 1966, preambular § 2, operative §§ 1, 2 (adopted with 91 yes votes, 0 no votes, 4 abstentions: http://unbisnet.un.org:8080 , last accessed 25 June 2017) and UNGA Res. 37/98 E, 13 December 1982, preambular § 3 (adopted with 83 yes votes, 22 no votes, 33 abstentions: UNBISnet, http://unbisnet.un.org:8080 , last accessed 25 June 2017). Back
¹⁴⁵ UNGA Res. 40/92 A, 12 December 1985, preambular § 5 (adopted with 93 yes votes, 15 no votes, 41 abstentions: UNBISnet, http://unbisnet.un.org:8080 , last accessed 25 June 2017). Back
¹⁴⁶ http://www.un.org/en/members/growth.shtml , last accessed 25 June 2017. Back

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ii. Call for Chemical Disarmament

In a resolution on "questions of general and complete disarmament” the General Assembly: “consider[ed] that the possibility of the use of chemical weapons […] constitutes a serious threat to mankind”. ¹⁴⁷

It went further in a resolution of 1969 stating that it was: “mindful […] that the prospects for general and complete disarmament […] and hence for peace throughout the world would brighten significantly if […] chemical […] agents intended for purposes of war […] were eliminated from all military arsenals”. ¹⁴⁸

120 of 126 UN member States voted in favour of the aforementioned resolution. However, it merely contemplates the benefits of chemical disarmament without envisioning any particular steps or referring to a legal obligation to refrain from the use of chemical weapons or dispose of respective arsenals. A shared commitment of that kind cannot be inferred. However, as has been observed in the section above, a strong legal opinion on the unlawfulness – whether in existence or in the future – of the use of chemical weapons seems to have prevailed.

In 1971, the General Assembly stated that it was “[c]onvinced of the importance and urgency of eliminating from arsenals of States, through effective measures, such dangerous weapons of mass destruction as those using chemical […] agents” and requested the Conference of the Committee on Disarmament to continue, “as a matter of high priority”, its negotiations with a view of reaching a comprehensive chemical disarmament agreement. ¹⁴⁹ At this point, the Assembly went a little further as it advocated for disarmament negotiations. Of the 132 UN member States 110 voted in favour of the resolution.

In the same vein, the UNGA in 1973:

[e]xpress[ed] its determination to act with a view to achieve effective progress towards general and complete disarmament, including the prohibition and elimination of all types of weapons of mass destruction such as those using chemical […] agents […]

[c]onsidering that chemical […] methods of warfare have always been viewed with horror and been justly condemned by the international community. ¹⁵⁰

A number of similar resolutions urging States and the relevant committees to pursue the aim of adopting a respective disarmament and verification regime have been adopted since. ¹⁵¹ These resolutions use a more compulsory language, fortifying the objective of chemical disarmament in

¹⁴⁷ UNGA Res. 2454 (XXIII) A, 20 December 1968, preambular § 2, operative § 6 (adopted with 107 yes votes, 0 no votes, 2 abstentions). Back
¹⁴⁸ UNGA Res. 2603 (XXIV) B, 16 December 1969, preambular § 5, operative §§ 1, 2 (adopted with 120 yes votes, 0 no votes, 1 abstention: UNBISnet, http://unbisnet.un.org:8080/ , last accessed 25 June 2017) and reaffirmed in UNGA Res. 2662 (XXV), 7 December 1970 (adopted with 113 yes votes, 0 no votes, 2 abstentions: Dag Hammarskjöld Library, ‘Resolutions adopted by the General Assembly at its 25th Session’, http://research.un.org/en/docs/ga/quick/regular/25). Back
¹⁴⁹ UNGA Res. 2827 A (XXVI), 16 December 1971, preambular § 2 operative §§ 2, 5 (adopted with 110 yes votes, 0 no votes, 1 abstention: http://www.un.org/depts/dhl/resguide/r26_resolutions_table_eng.htm). Back
¹⁵⁰ UNGA Res. 3077 (XXVIII), 6 December 1973, preambular §§ 2, 3, 4, 5 (adopted with 118 yes votes, 0 no votes, 0 abstentions: http://www.un.org/depts/dhl/resguide/r28_resolutions_table_eng.htm). Back
¹⁵¹ UNGA Res. 3256 (XXIX), 9 December 1974 (adopted by consensus: http://www.un.org/depts/dhl/resguide/r29_resolutions_table_eng.htm ); UNGA Res. 40/92 A, supra note 146, operative §§ 1–4 and C, operative §§ 1–4 (adopted with 93 yes votes, 15 no votes, 41 abstentions: http://www.un.org/depts/dhl/resguide/r40_resolutions_table_eng.htm ); UNGA Res. 41/58 B, 4 December 1986, operative §§ 1–4 (adopted with 100 yes votes, 11 no votes, 43 abstentions: http://www.un.org/depts/dhl/resguide/r41_resolutions_table_eng.htm ); UNGA Res. 43/74 A, 7 December 1988, operative § 3 and C, operative §§ 3, 5; UNGA Res. 44/115 B, 15 December 1989, operative §§ 3, 5; UNGA Res. 33/59, 14 December 1978, preambular §§ 9, 14, operative § 3 (adopted by consensus: Dag Hammarskjöld Library, ‘Resolutions adopted by the General Assembly at its 33rd Session’, http://research.un.org/en/docs/ga/quick/regular/33 ) and UNGA Res. 37/98 D, 13 December 1982, operative § 3 (adopted with 86 yes votes, 19 no votes, 33 abstentions: Dag Hammarskjöld Library, ‘Resolutions adopted by the General Assembly at its 37th Session’, http://research.un.org/en/docs/ga/quick/regular/37). Back

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a more comprehensive manner, and have high rates of approving votes. To a certain extent, they go beyond general declarations of intent to ban chemical weapons by means of legally binding documents. Combining the strongly worded characterization of chemical weapons use with the expressed determination to work towards a prohibition and general elimination shall be interpreted as a development worth noting regarding States’ opinion toward chemical weapons. However, while the number of votes in favour of these resolutions greatly outnumbered the votes against, often enough there was a notable amount of abstentions despite the general lack of legally binding force of UNGA resolutions.

In a 1972 resolution the UNGA “reaffirm[ed] the recognized objective of effective prohibition of chemical weapons” and invited States to observe obligations and accede to the Gas Protocol. ¹⁵²

In reaction to reports of instances of alleged use of chemical weapons the General Assembly requested and decided on impartial investigations to ascertain the relevant facts in 1980. ¹⁵³ Of the 154 UN members at the time, only 78 voted in favour despite the context between the resolution and the alleged chemical weapons use. At that point, the General Assembly called for proper action, which might explain the lack of support by about half the member States. No reference is made to general obligations under international law that may point to a customary rule.

B. UN Security Council

In 1987 the Security Council “deplore[d] […] the use of chemical weapons contrary to obligations under the 1925 Geneva Protocol” during the Iran-Iraq War. ¹⁵⁴ While the resolution was adopted unanimously it only referred to the Geneva Protocol and merely “deplored” where it could have condemned, thereby using rather weak language in reaction to an actual chemical weapons incident.

In 1991, the UNSC, after recalling that it was “[c]onscious […] of the statements by Iraq threatening to use weapons in violation of its obligations under the Geneva Protocol […] and of its prior use of chemical weapons and affirming that grave consequences would follow any further use by Iraq of such weapons”, in operative part C: “[d]ecide[d] that Iraq shall unconditionally accept the destruction, removal or rendering harmless, under international supervision, of […] [a]ll chemical and biological weapons and all stocks of agents”. ¹⁵⁵

This resolution goes very far in imposing substantive obligations on Iraq with regard to eliminating its chemical weapons stocks, which is most likely why it failed to be adopted unanimously. However, on the part of those States in favour of this substantial UNSC resolution, it points to opinio juris.

In a resolution of 2016 on the 1540 Committee the Security Council unanimously referred to the proliferation of (among others) chemical weapons as constituting a threat to international peace and security. ¹⁵⁶

¹⁵² UNGA Res. 2933 (XXVIII), 29 November 1972, operative §§ 1, 5. See also UNGA Res. 31/65, 21 December 1976 (adopted by consensus: Dag Hammarskjöld Library, ‘Resolutions adopted by the General Assembly at its 31st Session’ http://research.un.org/en/docs/ga/quick/regular/31 ) and UNGA Res. 32/77, 12 December 1977 (adopted by consensus: http://research.un.org/en/docs/ga/quick/regular/32). Back
¹⁵³ UNGA Res. 35/144 C, 12 December 1980, preambular § 5, operative §§ 1, 2, 4, 5 (adopted with 78 yes votes, 17 no votes, 36 abstentions: Dag Hammarskjöld Library, ‘Resolutions adopted by the General Assembly at its 35th Session’, http://research.un.org/en/docs/ga/quick/regular/35). Back
¹⁵⁴ UNSC Res. 598, 20 July 1987, preambular § 4 (adopted unanimously: http://www.casi.org.uk/info/undocs/scres/1987/598e.pdf). Back
¹⁵⁵ UNSC Res. 687, 3 April 1991, preambular § 8, operative §§ 7, 8 (adopted with 12 yes votes, 1 no vote (Cuba), 2 abstentions (Ecuador, Yemen): http://unispal.un.org/UNISPAL.NSF/0/FAB11BBFEA7E0B6585256C3F0065AEAE , last accessed 25 June 2017). Back
¹⁵⁶ UNSC Res. 2325, 15 December 2016, preambular § 2. Back

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C. Preliminary Conclusions

The UNGA had been stressing the importance of negotiating and adopting a comprehensive chemical disarmament treaty long before the CWC was adopted, as there was general agreement about chemical weapons being incompatible with the ‘accepted norms of civilization’ and an apparent conviction that their use should be unlawful. One needs to keep in mind, though, that resolutions containing such declarations of intent are easily adopted with high numbers of votes in favour as they do not contain hard commitments. This impression is confirmed by one of the listed resolutions which was adopted after an alleged use of chemical weapons and called for proper action. In that case, only about half of the UN members voted in favour of the respective UNGA resolution. However, there is a history of repetitive resolutions containing important opinio juris regarding chemical weapons use.

The UNGA makes no reference to any specific type of armed conflict. It can be inferred from the respective resolutions that for a number of decades preceding the adoption of the CWC, States showed a strong conviction that chemical weapon stocks should be disposed of completely. However, the question remains whether that is the case because the use of chemical weapons has been considered to be unlawful all this time, and if so, whether it was as a matter of customary law or whether such a disarmament regime was envisioned to render the use of chemical weapons unlawful under all circumstances and in all types of armed conflicts as a matter of treaty law.

What is interesting about the UNSC resolutions is that when it comes to reactions to actual incidents the obligations imposed on the respective State are often very far-reaching. However, even though actual events were being dealt with, unanimous adoption was not always achieved. One resolution concerning the Iran-Iraq War was adopted unanimously, but used much weaker language than one would expect under such circumstances.

However, overall, the analysis of the UNGA and UNSC resolutions has shown that a rather strong opinio juris seems to have prevailed with regard to the unlawfulness of the employment of chemical weapons for a long time already. While it may not have been expressed generally, it has been done so repeatedly and constantly, sometimes with reference to treaty law, sometimes without.

3. Multilateral Treaties

Both the ICTY and the ICTR have often resorted to the so-called sources-based approach, using international legal instruments as evidence of new customary international law. While this approach resembles the two-elements approach, both ad hoc tribunals usually did not prove the existence of opinio juris and State practice, but merely listed the international legal instruments and case law as evidence of either of these elements. ¹⁵⁷ This is a modification of the traditional approach as these sources can serve to prove both State practice and opinio juris. ¹⁵⁸ Because of the role of treaties that the International Law Commission has identified – “The fact that a rule is set forth in a number of treaties may, but does not necessarily, indicate that the treaty rule reflects a rule of customary international law” ¹⁵⁹ – the relevant treaties and instruments in the field at hand shall be examined in this section.

Treaties and instruments not addressing chemical weapons specifically, but just referring to principles relating to methods rather than means of warfare (e.g., the Geneva Conventions and their Protocols) are left out of this analysis. In order to show the evolution of treaties and other instruments regarding their focus, instruments applicable to both international and non-international armed conflicts will be analysed.

¹⁵⁷ B. Schlütter, Developments in Customary International Law (Boston, Martinus Nijhoff Publishers, 2010), p. 187. Back
¹⁵⁸ Id. , p. 188. Back
¹⁵⁹ ILC Report, supra note 16, draft conclusion 11(2). Back

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A. International Criminal Law Instruments

This sub-section analyses the relevant international criminal law instruments to show how they address the issue of chemical weapons use.

i. Statute of the Ad Hoc Tribunal for Yugoslavia

Both the ICTY and the ICTR were established by the United Nations Security Council acting under Chapter VII of the UN Charter. ¹⁶⁰ The statutes of the tribunals were not actually treaties, but were adopted by UNSC resolutions and have been amended by means of UNSC resolutions later on. They may nevertheless form the basis for conclusions on this matter.

The Statute of the International Tribunal for the Former Yugoslavia of 1993 only refers to means of warfare in Article 3 lit. a – naming the employment of poisonous weapons or other weapons calculated to cause unnecessary suffering as a violation of the laws or customs of war. The statute in Articles 2 and 3 makes strong reference – explicitly and implicitly – to the Geneva Conventions and the Hague Regulations. ¹⁶¹ Therefore, the statute merely refers to established humanitarian law that had already been in existence in the 19th and mid-20th century. The most likely explanation for this is that in order to ensure the legitimacy of the Tribunal, which was disputed from the beginning (culminating in an appeal passed against a judgment rendered by the Trial Chamber II in 1995), only offences well established under customary law were included in the statute. By that judgment, the appellant’s motion challenging the jurisdiction of the Tribunal had been denied. Before the Trial Chamber, the appellant had attacked the judgment with a three-pronged attack claiming illegal foundation of the ICTY, wrongful primacy of the Tribunal over national courts and lack of jurisdiction ratione materiae. ¹⁶² That decision was then appealed based on an alleged error of law. In October 1995, in the Decision on the Defence Motion for Interlocutory Appeal on Jurisdiction, the Chamber dismissed all of these grounds of appeal. ¹⁶³

The Chamber pointed out that, under Article 3 of its statute, the ICTY has jurisdiction over acts alleged in the indictment in question, regardless of whether they occurred within an internal or an international armed conflict. ¹⁶⁴ This statement reveals that the customary rules comprised in Article 3 of the statute are considered to be custom applicable to both international and non-international armed conflicts.

Due to its specific focus on genocide and crimes against humanity, the Statute of the International Criminal Tribunal for Rwanda of 1994 does not contain any provisions dealing with any specific weapons.

ii. Rome Statute of the International Criminal Court

Following the amendments adopted at the Kampala Review Conference of the Rome Statute of the ICC, the following acts are criminalized under the ICC Statute: employing poison or poisoned weapons; employing asphyxiating, poisonous or other gases, and all analogous liquids, materials or devices in non-international armed conflicts (Arts. 8 II(e)(xiii) and (xiv)). ¹⁶⁵ Only 21 States have ratified the amendment so far. ¹⁶⁶ In its non-amended version the ICC Statute prohibits the employment of the exact same types of weapons in international armed conflicts only (Arts. 8 II(b)(xvii) and (xviii)).

¹⁶⁰ UNSC Res. 827, 25 May 1993 establishing the ICTY and UNSC Res. 955, 8 November 1994 establishing the ICTR. Back
¹⁶¹ Cf. R. Heinsch, Die Weiterentwicklung des humanitären Völkerrechts durch die Strafgerichtshöfe für das ehemalige Jugoslawien und Ruanda: Zur Bedeutung der internationalen Gerichtsentscheidungen als Rechtsquelle des Völkerstrafrechts (Berlin, Berliner Wissenschafts-Verlag, 2007), p. 67. Back
¹⁶² Prosecutor v Tadić, supra note 31, §§ 1–2. Back
¹⁶³ Id. , §§ 48, 64, 145. Back
¹⁶⁴ Id. , § 137. Back
¹⁶⁵ Rome Statute of the International Criminal Court (1998). Back
¹⁶⁶ Amendment to Article 8 of the Rome Statute of the International Criminal Court, Kampala, 10 June 2010, U.N.T.S No. 2868. Back

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The ICC Statute, which entered into force in 2002, currently has 124 State parties – of which 25 have made certain declarations to it – and 31 signatories. ¹⁶⁷ Of those declarations, only the French reservation needs to be considered as it represents an interpretative declaration regarding Article 8 II(b) in which France reserves the right to use any kind of weapon for purposes of self-defence if it considers it necessary to do so. ¹⁶⁸

B. International Humanitarian Law Treaties

The following sub-section examines humanitarian law treaties relevant to the matter at hand. Even though not all of them apply to non-international armed conflicts, they are analysed because they may give valuable insights into how international law regarding chemical weapons has evolved over time. This may, in turn, be valuable for conclusions regarding the research question.

i. Declaration Concerning Asphyxiating Gases of 1899 ¹⁶⁹

After the adoption of the 1675 Strasbourg Agreement limiting the use of poison bullets and the 1874 Brussels Convention on the Law and Customs of War prohibiting the employment of poison or poisoned weapons, the Declaration Concerning Asphyxiating Gases was signed in 1899 at the First Hague Peace Conference. Upon ratification: “[t]he Contracting Powers agree to abstain from the use of projectiles the sole object of which is the diffusion of asphyxiating or deleterious gases”. ¹⁷⁰ It is further specified that the declaration “is only binding on the Contracting Powers in the case of a war between two or more of them”, i.e. in international armed conflicts.

The Declaration entered into force in 1900 and is still in force; no reservations have been filed. ¹⁷¹ Currently, there are 33 State parties to the treaty representing all the continents and UN Regional Groups. ¹⁷²

ii. Hague Convention IV Respecting the Laws and Customs of War on Land of 1907 ¹⁷³

Article 22 of Hague Convention IV addresses the issue of means of warfare in a general manner: “The right of belligerents to adopt means of injuring the enemy is not limited.” Article 23 lit. a further qualifies this by declaring certain means such as “poison or poisoned weapons” as “especially forbidden”. The Convention applies to international armed conflicts only (Art. 2).

It is still in force, with 38 State parties and 15 signatories to this day, which are representative of the UN Regional Groups. ¹⁷⁴ The reservations made to the Convention are irrelevant for the provisions in question.

¹⁶⁷ ICRC, supra note 8. Back
¹⁶⁸ ICRC, ‘Treaties, States Parties and Commentaries – By Topic’, https://www.icrc.org/. Back
¹⁶⁹ Referred to as Declaration IV.2. Back
¹⁷⁰ The Declaration (IV.2) does not contain any numbered articles or paragraphs. Back
¹⁷¹ ICRC, ‘Treaties States Parties and Commentaries – By Topic’, https://www.icrc.org/. Back
¹⁷² Id. Back
¹⁷³ According to Article 4, this Convention substitutes the Convention of 1899 as between the Contracting Powers of the more recent treaty. Back
¹⁷⁴ ICRC, ‘Treaties, States Parties and Commentaries – Convention (IV) respecting the Laws and Customs of War on Land and its Annex: Regulations concerning the Laws and Customs of War on Land, The Hague, 18 October 1907’, https://www.icrc.org/applic/ihl/ihl.nsf/INTRO/195. Back

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iii. Protocol for the Prohibition of the Use of Asphyxiating, Poisonous or Other Gases, and of Bacteriological Methods of Warfare of 1925

During the First World War, the Allies failed to protest the widespread use of gas by Germany. This may have been because at that time, no belief in the illegality of such battlefield behaviour had formed yet. ¹⁷⁵

When Japan was accused of using tear, vomiting and mustard gas as well as blister agents against Chinese troops during the Sino-Japanese war, ¹⁷⁶ the League of Nations Council adopted a resolution in 1938: “recall[ing] that the use of toxic gases is a method condemned by international law, which cannot fail, should resort be had to it, to meet the reprobation of the civilised world”. ¹⁷⁷

Between the First World War and the mentioned armed conflicts – albeit of an international character – the Geneva Protocol was adopted. It prohibits the “use in war of asphyxiating, poisonous or other gases, and of all analogous liquids, materials or devices”. The parties to the Protocol “agree[d] to be bound as between themselves”, ¹⁷⁸ i.e. in international armed conflicts between State parties.

The Protocol entered into force in 1928 and is still in force. ¹⁷⁹ There are currently 140 State parties to the Protocol, of which 23 have made reservations to it, ¹⁸⁰ intending to clarify that parties to the Protocol only consider themselves bound by it in relation to other States which have ratified it and that they do not consider themselves bound by it in relation to a State whose forces do not respect the prohibitions of the Protocol.

There are still reservations to the Protocol which have not been withdrawn, although most of the respective States are now parties to the CWC. While it can be argued that those reservations are technically still valid, some claim that the general prohibitions of Article I in conjunction with Article XXII proscribing reservations to any articles of the CWC have the effect of rendering void all previous reservations to prohibitions on the use of chemical weapons by entry into force of or accession to the Convention. ¹⁸¹ Whereas it is indeed contradictory to be a State party to this Convention and uphold the right to reprisals under the Gas Protocol, such behaviour could be an indication of certain opinio juris. ¹⁸² It is rather more likely, though, that States acceding to the CWC did not deem it necessary to clarify their commitment to the regulations of the Convention since it applies as lex posterior to instances within an international armed conflict and has a broader scope of application encompassing non-international armed conflict situations as well.

According to scholars the Geneva Protocol came to reflect customary international law decades ago, ¹⁸³ at least with regard to lethal chemical weapons. ¹⁸⁴ A number of States have also expressed the view that the content of the prohibition inherent in the Geneva Protocol has developed into

¹⁷⁵ Thomas and Thomas, supra note 26, p. 140. Back
¹⁷⁶ L. Szinicz, ‘History of Chemical and Biological Warfare Agents’, Vol. 214 No. 3 Toxicology 2005, p. 170. Back
¹⁷⁷ League of Nations Council Res. 14 May 1938, Pt. II. Back
¹⁷⁸ Protocol for the Prohibition of the Use of Asphyxiating, Poisonous or Other Gases, and of Bacteriological Methods of Warfare, supra note 138, § 1. Back
¹⁷⁹ ICRC, ‘Treaties, States Parties and Commentaries – Protocol for the Prohibition of the Use of Asphyxiating, Poisonous or Other Gases, and of Bacteriological Methods of Warfare, Geneva, 17 June 1925’, https://www.icrc.org/ihl/intro/280. Back
¹⁸⁰ ICRC, ‘Treaties, States Parties and Commentaries’, https://www.icrc.org/. Back
¹⁸¹ W. Krutzsch, ‘Article I’, in W. Krutzsch et al. (eds), The Chemical Weapons Convention: A Commentary (Oxford, OUP, 2014), p. 66. Back
¹⁸² Hayashi, supra note 4, p. 84. Back
¹⁸³ R. R. Baxter and T. Buergenthal, ‘Legal Aspects of the Geneva Gas Protocol of 1925’, Vol. 64 No. 5 A.J.I.L. 1970, p. 853 and see also Y. Dinstein, ‘Customary International Law and the Prohibition of Use of Weapons of Mass Destruction’, in G. Gasparini and N. Ronzitti (eds.), The Tenth Anniversary of the CWC’s Entry into Force: Achievements and Problems (Rome, Instituto Affari Internazionali 2007) p. 94. Back
¹⁸⁴ Baxter and Buergenthal, supra note 183, p. 853. Back

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reflecting customary international law. ¹⁸⁵ In a 1969 UNGA resolution it was: “recognize[d] […] that the Geneva Protocol embodies the generally recognized rules of international law prohibiting the use in international armed conflicts of all […] chemical methods of warfare”. ¹⁸⁶ Two resolutions recall: “the provisions of the [1925 Geneva Convention], and other relevant rules of customary law” . ¹⁸⁷

One needs to keep in mind, though, that the Geneva Protocol only applies in relations between States. Even if the content of the Protocol had developed into a customary rule, this would not answer the research question at hand entirely.

iv. Convention on Prohibitions or Restrictions on the Use of Certain Conventional Weapons Which May be Deemed to be Excessively Injurious or to Have Indiscriminate Effects of 1980

Originally, the Conventional Weapons Convention (1980, entry into force 1993) and its annexed Protocols were to apply to international armed conflicts, but were amended in 2001 to apply to non-international armed conflicts as well (Article 1(1) Amendment of Article 1 of the CCW Convention). The amendment has been ratified by 83 of the 123 State parties and 5 signatories of the Convention. ¹⁸⁸

Annexed Protocol III on “Prohibitions or Restrictions on the Use of Incendiary Weapons Protocol” does not impose a general prohibition to use incendiary weapons (which, according to the definition of Article 1(1) of the Protocol can, but does not necessarily have to be a type of chemical weapon) on State parties, but proscribes the use of such means against civilians and civilian objects directly and against military objectives located within a concentration of civilians (Art. 2). The rule represents a reinforcement of the principle of distinction rather than a general prohibition of incendiary weapons.

12 of the parties to the Convention have made reservations to it (the Netherlands even made two reservations), none of which are relevant for the matter at hand. ¹⁸⁹ Protocol III, which also entered into force in 1983, has been ratified by 113 States representing the five Regional Groups of the UN. ¹⁹⁰

v. Convention on the Prohibition of the Development, Production, Stockpiling and Use of Chemical Weapons and on Their Destruction of 1993

The Chemical Weapons Convention, which entered into force in 1997, is applicable to both international and non-international armed conflicts as Article I does not differentiate between different types of conflicts. ¹⁹¹ There are 192 State parties and 1 State signatory to the

¹⁸⁵ The ICRC Study, supra note 11, Vo. II, Ch. 24 names 10 States: §§ 144, 150, 160, 196, 343, 347, 375, 379, 389, 420. At the same time, Denmark, in 1969, objected the view that the content of the Gas Protocol had developed into customary law: id., § 201. See also Tabassi, supra note 59, p. 2. Back
¹⁸⁶ UNGA Res. 2603 (XXIV) A, 16 December 1969, preambular § 5. Back
¹⁸⁷ UNGA Res. 42/37 C, 30 November 1987, preambular § 1 and UNGA Res. 43/74, 7 December 1988, preambular § 5 (emphasis added). Back
¹⁸⁸ ICRC, ‘Treaties, States Parties and Commentaries – Convention on Prohibitions or Restrictions on the Use of Certain Conventional Weapons Which May be Deemed to be Excessively Injurious or to Have Indiscriminate Effects, Geneva, 10 October 1980’, https://www.icrc.org/ihl/INTRO/500?OpenDocument. Back
¹⁸⁹ https://www.icrc.org/ihl/INTRO/500?OpenDocument ; https://www.icrc.org/ , last accessed 25 June 2017. Back
¹⁹⁰ ICRC, ‘Treaties, States Parties and Commentaries – Protocol on Prohibitions or Restrictions on the Use of Incendiary Weapons (protocol III), Geneva, 10 October 1980’, https://ihl-databases.icrc.org/. Back
¹⁹¹ Blake and Mahmud, supra note 4, p. 253. Back

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Convention, ¹⁹² making it a virtually universal treaty. 21 of the parties have made reservations to it, ¹⁹³ none of which refers to the use of chemical weapons.

The CWC contains a definition of the term ‘chemical weapons’ for the purposes of the general obligations under Article I(1) CWC which prescribes inter alia: “Each State Party to this Convention undertakes never under any circumstances […] to use chemical weapons”. In Article II, it is laid out that chemical weapons:

means the following, together or separately: toxic chemicals and their precursors, […] munitions and devices, specifically designed to cause death or other harm through the toxic properties of those toxic chemicals […], any equipment specifically designed for use directly in connection with the employment of [these] munitions and devices. ¹⁹⁴

The Chemical Weapons Convention’s annexes contain a list of agents which are damaging to the human body in a permanent or non-permanent way, but are not lethal under regular circumstances. Article II of the CWC sets out the intended purpose as the ultimate criterion for defining a toxic chemical as a chemical weapon. ‘Toxic chemical’ is defined as: “[a]ny chemical which through its chemical action on life processes can cause death, temporary incapacitation or permanent harm to humans or animals” (Art. II(2)). According to this concept, all toxic or precursor chemicals are regarded as chemical weapons unless they have been developed, produced, stockpiled, or used for purposes not prohibited. The definition thus covers any toxic or precursor chemicals intended for chemical weapons purposes, irrespective of whether it has been listed in one of the schedules annexed to the CWC. However, the Convention takes a negative approach by only defining four purposes not prohibited under the Convention (Art. II(9)). Under this Convention, toxicity only relates to human beings and animals. Chemicals predominantly affecting plant life such as herbicides and defoliants are not covered by the Convention’s provisions relating to ‘chemical weapons’. ¹⁹⁵ Article II(1) makes it clear that toxicity is not restricted to lethality. ¹⁹⁶ Schedule 1 chemicals pose the highest risk of the three categories to the purposes of the CWC as they have few if any peaceful purposes. Schedule 2 chemicals pose a significant risk to the Convention’s purposes either because they can be used themselves as chemical weapons or because of their role as precursors to schedule 1 or 2 chemicals. Schedule 3 chemicals are produced in large quantities commercially but pose a risk to the Convention because of their role as precursors to either schedule 1 or 2 chemicals. ¹⁹⁷ Certainly not all the chemicals listed in the three schedules annexed to the CWC have come to be forbidden under customary law.

State parties to the CWC agreed not to use chemical weapons and not to “develop, produce, otherwise acquire, stockpile or retain chemical weapons, or transfer, directly or indirectly, chemical weapons to anyone” (Art. I(1)(a) CWC), to “destroy chemical weapons it owns or possesses, or that are located in any place under its jurisdiction or control”, to “destroy all chemical weapons it abandoned on the territory of another State Party” and to “destroy any chemical weapons production facilities it owns or possesses, or that are located in any place under its jurisdiction or control” (Art. I(1)(a), Arts. I(2)–(4)). This wording of the chapeau of Article I(1) points to the universal character of an extraordinarily comprehensive prohibition which encompasses all activities of State parties everywhere and which excludes any kind of justification

¹⁹² ICRC, ‘Treaties, States Parties and Commentaries – Convention on the Prohibition of the Development, Production, Stockpiling and Use of Chemical Weapons and on their Destruction, Paris, 13 January 1993’, https://ihl-databases.icrc.org/ihl/INTRO/553?OpenDocument. Back
¹⁹³ ICRC, supra note 181. Back
¹⁹⁴ The way States decided to define the term ‘chemical weapon’ marks a change from past practice of defining a weapon in international agreements. Typically, a weapon is considered to be the entirety of its components, characterized by certain criteria and characteristics that would allow for a distinction between the types of weapons covered by a treaty and those types not covered by it. However, in the CWC, each of the components of a chemical weapons system in itself is regarded as a chemical weapon: see Krutzsch et al., supra note 181, Art. II, pp. 23-24. Back
¹⁹⁵ However, their use against plant life in armed conflict is prohibited under the Geneva Protocol. Back
¹⁹⁶ Krutzsch et al., supra note 181, Article II, pp. 77–79. Back
¹⁹⁷ Kelle, supra note 74, p. 130. Back

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for the activities listed under subparagraphs a–d. ¹⁹⁸ Agreeing to not use chemical weapons (without making a distinction between international and non-international conflicts), but also to get rid of the possibility of pulling them out of storage and doing so by destroying them and their production facilities shows a clear intention to eliminate chemical weapons entirely.

Furthermore, the CWC refers to non-lethal riot control agents which CWC State parties shall: “undertake not to use […] as a method of warfare” (Art. I(5) CWC). However, Article II(9)(d) allows for the employment of such agents for law-enforcement purposes, including domestic riot control. Consequently, recourse to non-lethal chemical agents such as tear gas is not permissible in the context of armed conflicts, but domestically under certain circumstances. ¹⁹⁹

All of these aspects of the CWC add up to a strong expression of opinio juris of the parties that the use of chemical weapons shall be unlawful in armed conflicts under any circumstances. State parties have agreed to very far-reaching obligations under the CWC, thereby limiting their sovereign scope of decision-making and action to a significant extent. ²⁰⁰ States have suited the action to the word since, by December 2015, 91 % of declared Category 1 (‘Schedule 1’ chemicals in the terminology of the Annex on Chemicals of the CWC as explained above) chemicals had been destroyed. ²⁰¹

C. Preliminary Conclusions

Some valuable lessons can be drawn from the analysis of treaties. The theory of public international law teaches us that treaties may serve as acts of practice significant for the development of custom ²⁰² as well as reflections of opinio juris. If a number of States make a habit of concluding treaties which contain certain standard provisions, this may, under suitable circumstances, be taken to show that they recognize the existence of a custom requiring them to act or not act in a certain way. While multilateral treaties are documents whose wording is strongly shaped by political negotiations, the fact that the treaties analysed above were signed and ratified by States eventually shows that overall they do reflect States’ opinion that chemical weapons shall be banned and that the use of those means is to be refrained from or shall be criminalized respectively.

For decades, long before the implementation of a general ban on chemical weapons and the beginning of systematic chemical disarmament in the context of the CWC, a large number of States have shown their conviction that chemical weapons use shall be banned. A long practice of the creation of treaties rendering the use of certain means that qualify as chemical weapons unlawful has been shown. What has also been shown is the evolution of humanitarian law treaties that were first applicable to international armed conflicts only, to a treaty that was first applicable to international armed conflicts only, then amended to be applicable to non-international armed conflicts as well (CCW), to the CWC – a treaty designed to be applicable to both types of treaties from the beginning. The CWC marks a new level of commitment with regard to both types of conflict. Furthermore, as has been shown above, resolutions adopted in the UN General Assembly and Security Council have gone through a development in which the distinction between international and non-international armed conflicts became less and less important when dealing with unlawful means of warfare.

The CWC is also remarkable in that it renders not only the use, but also the development, production, acquisition, stockpiling, retention and transfer of chemical weapons unlawful. State

¹⁹⁸ Krutzsch et al., supra note 181, Article I, p. 65. Back
¹⁹⁹ Dinstein, supra note 183, pp. 95–96. Back
²⁰⁰ J. D. Fry, ‘Sovereign Equality under the Chemical Weapons Convention: Doughnuts over Holes’, Vol. 15 J.C.S.L. 2010, pp. 58–59. Back
²⁰¹ OPCW, Report of the OPCW on the Implementation of the Convention on the Prohibition of the Development, Production, Stockpiling and Use of Chemical Weapons and on their Destruction in 2015, OPCW Doc. C-21/4, 30 November 2016, p. 1. Back
²⁰² Thirlway, ‘The Sources of International Law’, in M. D. Evans (ed.), International Law (Oxford, OUP, 2010, 3rd ed.), p. 111. Back

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parties are also not allowed to engage in military preparations to use chemical weapons or to assist, encourage or induce, in any way, anyone to engage in any activity prohibited to a State party under the Convention. Therefore, the CWC comprises the most comprehensive rules and widest scope of application concerning chemical weapons yet. At this point the CWC has been ratified almost universally. Regarding the type of materials covered, the CWC also marks a new phase, as lethality is not a precondition for a prohibition under the Convention. The definition of chemical weapons covered by the CWC refers to chemicals which can cause death, temporary incapacitation or permanent harm to humans or animals.

The ICC Statute and the CWC were adopted in the late 1990s. It is worth noticing that while almost all States have acceded to the latter instrument, thus accepting the prohibition on the use of chemical weapons in international and non-international armed conflicts, far fewer States go as far as having their use in international armed conflicts (let alone non-international ones) criminalized. Apparently, it still makes a difference for States whether they merely declare their willingness to abandon chemical weapons, or whether such acts are criminalized at the international level and jurisdiction over them is granted to an international court, most likely for reasons of sovereignty. However, by means of Articles 12 and 13 of the Statute – which parties to the treaty agreed on – jurisdiction may still be exercised over the crimes in question even without ratification of the relevant amendment.

While there have not been a lot of incidents involving the use of chemical weapons in non-international armed conflicts, it would be inappropriate to speak of an ‘almost complete abstention’ since the Second World War. However, despite the large stocks of chemical weapons, especially before the CWC was adopted – and stocks have been eliminated under OPCW supervision – they were used in Iraq and Syria “only”. ²⁰³ There they were and – in the case of the latter – are in fact still used and the reactions by individual members of the international community were sometimes not as explicit in condemning them as one may expect. As the ICJ has established in the Nicaragua judgment, though, perfect practice is not necessary for the establishment of a customary rule.

At this point, recalling the particularities of prohibitive rules of customary law as well as of provisions in the field of International Humanitarian Law is in order. When assessing whether a customary rule has come into existence, an examination of both physical and verbal practice shall be conducted. It has been established by international courts that with regard to IHL particular reliance needs to be put on verbal practice. When analysing the verbal practice concerning the use of chemical weapons (including the statements by those who have evidently or most likely employed chemical weapons but then denied and negated such physical practice) one needs to come to the conclusion that verbal practice is indeed virtually uniform on the matter at hand. The international community has made it abundantly clear – not just by means of individual and common statements, but also by backing fact-finding missions and strongly worded Security Council resolutions bearing actual consequences – that the instances of chemical weapons use are considered to be breaches of a rule. With regard to the density requirement concerning practice, the nature of prohibitive rules must be taken into account. Because of their nature, the standard applied towards non-prohibitive rules cannot strictly be applied to the previous, since the amount of physical practice will be smaller in almost every case. As to the question whose practice and opinio juris is more relevant, it has been observed that even possessor States of chemical weapons such as Russia and the US have participated in common acts of State practice and expressions of opinio juris against the use of such means of warfare. Since the Chemical Weapons Convention has been universally ratified no State has exempted from that participation, although admittedly, Syria has derogated from its obligations extensively, thus proving once again that perfect practice can hardly be achieved. However, Syria’s constant denial to have employed chemical weapons reliance needs to be put on verbal practice. When analysing the verbal practice concerning the use of chemical weapons (including the statements by those who have evidently or most likely employed chemical weapons but then denied and negated such physical practice) one needs to come to the conclusion that verbal practice is indeed virtually uniform on the matter at hand. The international community has made it abundantly clear – not just by means of individual and common statements, but also by backing fact-finding missions and strongly worded Security Council resolutions bearing actual consequences – that the instances of chemical weapons use are considered to be breaches of a rule. With regard to the density requirement concerning practice, the nature of prohibitive rules must be taken into account. Because of their nature, the standard applied towards non-prohibitive rules cannot strictly be applied to the previous, since the amount of physical practice will be smaller in almost every case. As to the question whose practice and opinio juris is more relevant, it has been observed that even possessor States of chemical weapons such as Russia and the US have participated in common acts of State practice and expressions of opinio juris against the use of such means of warfare. Since the Chemical Weapons Convention has been universally ratified no State has exempted from that participation, although admittedly, Syria has derogated from its obligations extensively, thus proving once again that perfect practice can hardly be achieved. However, Syria’s constant denial to have employed chemical weapons

²⁰³ T. McCormack, ‘International Law and the Use of Chemical Weapons in the Gulf War’, Vol. 21 California Western International Law Journal 1990, pp. 12–16. Back

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and statements by its representatives acknowledging its obligations under the Convention ²⁰⁴ show that even Syria acknowledges the existence of some kind of norm prohibiting such actions.

The CWC is a very recent, highly specific treaty which has been applicable to both types of conflicts since its entry into force. As has been shown, it is much more comprehensive than the other treaties, in that it does not only refer to the use of chemical weapons and in that it contains a comprehensive list of prohibited chemical agents. According to the ICJ North Sea Continental Shelf cases, there are three types of potential relationships between customary law and treaties. A treaty may be declaratory (codify) of a customary norm, it may crystallize a norm or, after the adoption of a treaty, a provision may be accepted and followed by States as custom in their practice. ²⁰⁵ The ILC has mirrored these findings in its conclusions on the establishment of customary international law. ²⁰⁶

The CWC marks a significant evolution with regard to the research question of this paper. It does not only prohibit the use of chemical weapons under any circumstances, but also a range of activities that would promote the use or enable actors to employ chemical weapons. The Convention hence marks a preliminary high point in the development of disarmament treaties and other legal instruments prohibiting the use of certain means of warfare.

With this in mind, one needs to wonder whether the Chemical Weapons Convention marks the declaration of an already existing norm on the prohibition of the use of chemical weapons – including in non-international armed conflicts – or the crystallization of such a norm. Applying the findings of the ICJ in the North Sea Continental Shelf cases, it is reasonable to conclude that the relevant prohibitive norm enshrined in the Geneva Convention – whose application has undergone an extension from a rule merely applicable to international armed conflicts to one that was also referred to when non-international armed conflicts were concerned – has crystallized into a rule of customary international law, at the latest, by means of the adoption of the CWC.

However, because Article I of the Convention goes much further concerning the obligations it imposes on States, the scope of the customary rule established in the previous paragraph cannot cover the scope of said provision. At best, the CWC has set into motion the development of an even broader rule of customary international law concerning prohibitions relating to chemical weapons. However, it goes beyond the scope of this paper to develop comprehensive thoughts on the potentially norm-creating character of the CWC with respect to the scope of this prohibitive rule.

As to the scope of the established prohibitive rule, it has been observed that the limitations and prohibitions regarding the use of poison/poisoned weapons as well as asphyxiating and poisonous gases and analogous devices date back several centuries. The Geneva Protocol referred to other types of gases, too, but until then, the respective prohibitions only applied to international armed conflicts. The International Humanitarian Law treaties of the 19th and earlier 20th century were not applicable to non-international armed conflicts. A lot of them focused on poisoned weapons and asphyxiating gases. The Geneva Protocol of 1925 marked a change and a step forward in that it comprises poisonous and asphyxiating gases as well as all analogous liquids, materials and devices. The ICTY and the ICC Statute both refer to poisoned/poisonous weapons. The ICC Statute further mentions asphyxiating, poisonous or other gases, and all analogous liquids, materials or devices – thus making use of language established in the Geneva Gas Protocol and representing the common denominator. ²⁰⁷

²⁰⁴ See, e.g., UNSC Meetings Coverage, Security Council Fails to Adopt Resolution Condemning Chemical Weapons Use in Syria, Following Veto by Russian Federation, UN Doc. SC/12791, 12 April 2017. Back
²⁰⁵ North Sea Continental Shelf Case, supra note 21, p. 38, §§ 62 et seq. Back
²⁰⁶ ILC Report, supra note 16, draft conclusion 11. Back
²⁰⁷ One should be mindful, though, that a type of ‘poison’ as such can, but does not necessarily have to contain chemical components. Back

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States have made it a habit to conclude treaties which render the use of poison, poisonous weapons as well as the employment of asphyxiating, poisonous or other gases, and all analogous liquids, materials or devices unlawful with regard to international armed conflicts.

At this point, it can therefore be concluded that the content of the Geneva Protocol relating to the characteristics of chemicals to be forbidden as chemical weapons (‘asphyxiating, poisonous or other gases, and of all analogous liquids, materials or devices’) has developed into custom for both international and non-international armed conflicts. ²⁰⁸

V. Conclusions

It needs to be acknowledged that treaty law has indeed mostly developed the way the ‘Tadić logic’ describes – into a direction where a distinction between rules applicable to international and non-international armed conflicts becomes less and less important. This has been shown with regard to the Conventional Weapons Convention as well as the Chemical Weapons Convention. Whereas the provisions on certain chemical weapons of the ICC Statute in its initial version did not apply to non-international conflicts, this general development has continued by means of the Kampala amendments. However, as the analysis above has shown, overall, States seem more inclined to uphold this distinction when it comes to having certain actions not just prohibited, but criminalized and the jurisdiction over respective incidents conferred to international courts.

The joint action taken in the shape of the creation of fact-finding missions and the Joint Investigative Mechanism regarding the incidents in Syria whose mandate and competencies are/were significantly broader than those of similar missions that preceded it have been very powerful reactions as well. The establishment of such bodies clearly marks the statement that the use of chemical weapons will not be tolerated and left uncommented by the international community. While there has not been a very large amount of physical practice, there has been a lot of verbal practice and expressions of opinio juris have been produced in this regard. Even though the UN Security Council failed to extend the mandate of the JIM in late 2017, one has to acknowledge that none of the States responsible for the drafts remaining only drafts were ambiguous about their attitude towards chemical weapons use. Verbal practice and expressions of opinio juris have remained in line with the development described above. The same holds true for the reaction towards the Khan Shaykun incident.

As the analysis above has shown, the content of the Geneva Protocol relating to the characteristics of chemicals to be forbidden as chemical weapons (‘asphyxiating, poisonous or other gases, and of all analogous liquids, materials or devices’) has developed into custom for both international and non-international armed conflicts – at the latest by means of the Chemical Weapons Convention.

While the international community has come a long way since the first large-scale employment of chemical weapons in the shape of a chlorine gas attack at Ypres in 1915 by Germany, ²⁰⁹ there are still a number of steps to be taken until general chemical disarmament can be achieved. Respective disarmament activities shall not be undermined by setbacks resulting from current events. Also, the issue of dual use chemicals that has been discussed for a long time is being systematically dealt with, among others, by the Australia Group. The Group is a forum of 41 States and the European Union as an institution which, by means of harmonizing export controls, seek to ensure that exports do not contribute to the development of chemical and biological weapons. ²¹⁰

²⁰⁸ Tabassi, supra note 59 , p. 3; Boothby, supra note 36, p. 199 and S. E. Freeman and H. O. Smith, ‘War and International Humanitarian Law’, Vol. 13 No. 2 Medicine, Conflict and Survival 1997, p. 118. Back
²⁰⁹ Thomas and Thomas, supra note 26, p. 139. Back
²¹⁰ The Australia Group, http://australiagroup.net/en/index.html . See also Himmel et al., ‘Eine Welt ohne Chemiewaffen? Herausforderungen für das CWÜ’, Vol. 35 Wissenschaft und Frieden 2017, p. 53. Back

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After a failed attempt at a UN Security Council referral to the ICC of the situation in Syria in May 2014, ²¹¹ the international community should consider all available options provided for by the Rome Statute of the International Criminal Court, in order to ensure accountability. A legal evaluation of such options in the light of the current political ramifications may be the subject of future research.

²¹¹ UNSC Meetings Coverage, Referral of Syria to International Criminal Court Fails as Negative Votes Prevent Security Council from Adopting Draft Resolution, UN Doc. SC/11407, 22 May 2014. Back

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