The Controversy Around Chemical Warfare, Chemical Weapons and Their Prohibition

Photo: British troops blinded by tear gas at the Battle of Estaires, Imperial War Museum.


Russia’s invasion of Ukraine has been testing the international legal norms on the use of force and conduct of warfare since day one, and the weaponry employed by Russia is no exception.

Reports have surfaced of three instances, in April, September, and October 2022, in which Russian forces may have deployed chemical munitions in Ukraine, prompting international concern. These Reports have suggested that tear gas may have actually been used. Tear gas is a “riot control agent,” prohibited “as a method of warfare,” and its use may well have been intended to make identification of any chemical agents deployed more difficult or pave the way for use of more lethal chemical agents (see the precedents of Syrian chemical attacks using mixtures of tear gas and nerve agents).  At the same time, state officials and analysts continue to warn of the threat of Russian chemical weapons attacks in Ukraine, either as a false flag attack or in response to the loss of territory in Ukraine

Moreover, in April 2022, the UK Ministry of Defense announced that Russia had used white phosphorus (“WP”) munitions in Ukraine’s Donetsk Oblast.  Ukrainian authorities have also accused Russia of deploying WP bombs in the suburbs of Kyiv and at other sites across Ukraine – though some suggest that other weapons with incendiary effects were actually used in these attacks.

This post examines how International Humanitarian Law (“IHL”) regulates the use of chemical weapons, including riot control agents like tear gas, and of WP munitions, and what may be done when the use of such weapons is alleged.

Chemical Weapons – Absolute Prohibition Under IHL

Chemical weapons, including choking, blistering, blood and/or nerve agents, like chlorine or mustard gas, arsine, and sarin, are a particularly gruesome tool of warfare, which cause indiscriminate death and suffering.

In international law, the 1925 Geneva Gas Protocol and the 1993 Chemical Weapons Convention (“CWC”) set forth a prohibition on chemical warfare. Russia and Ukraine are each Parties to both the 1925 Geneva Gas Protocol (see Ukraine; Russia) and the CWC (see Ukraine; Russia), and thus bound by these instruments. 

The prohibition on the use of chemical weapons, and of riot control agents as a method of warfare, is also considered to reflect customary international law (for chemical weapons; for riot control agents), applicable in both international and non-international armed conflicts.  The use of chemical weapons in both international and non-international armed conflicts is also arguably a war crime within the jurisdiction of the International Criminal Court (“ICC”), pursuant to Article 8(2)(b)(xvii) and 8(2)(e) of the Rome Statute.

The CWC imposes a ban on the use of chemical weapons (as defined in Article II CWC)under any circumstances’, as well as on their development, production, acquisition, stockpiling, transfer, and retention. It also prohibits State Parties from using riot control agents as a method of warfare. The CWC further obliges State Parties to declare and destroy their chemical weapons stockpiles, and destroy or retire the facilities producing them.

Under the CWC, both Russia and Ukraine are subject to a complete ban on the development and use of chemical weapons under any circumstances, and against any targets – military or civilian.  Both states are also prohibited from using riot control agents like tear gas as a means of warfare.

White Phosphorus Munitions – What They Are And Are Not, And How IHL Treats Them

White phosphorus (“WP”) is a toxic, colorless, or whiteish-waxy material manufactured from phosphate rocks, which ignites on contact with oxygen, producing light, thick clouds of white smoke, and temperatures high enough to burn through metal. In military applications, WP is used to illuminate targets, or obscure personnel movement through smokescreens. When deployed as a weapon, WP causes horrific burns.

WP munitions do not squarely qualify either as chemical or incendiary weapons under applicable treaties, namely the 1925 Geneva Gas Protocol, the CWC and the Protocol on Prohibitions or Restrictions on the Use of Incendiary Weapons (see arguments for and against their treaty classification as either type of weaponry). 

First, WP munitions are not among the “asphyxiating, poisonous or other gases, and of all analogous liquids, materials or devices” covered by the 1925 Geneva Gas Protocol, since the prime purpose of WP is not to gas, asphyxiate, or poison, but to illuminate or obscure – while their harmful and weaponized side-effect is also not poisonous or asphyxiating, but incendiary.

Second,  WP munitions are not “chemical weapons” under Article II of the CWC, since they are not “specifically designed to cause death or other harm” by means of a “toxic chemical,” which causes “death, temporary incapacitation or permanent harm […] through its chemical action on life processes” (emphasis added). WP instead causes harm to humans through its thermal properties. Moreover, WP munitions are principally designed as obscurants and illuminants, and thus also fall under the carveout of Article II(9)(c) of the CWC on toxic chemicals used for purposes not prohibited under the CWC, namely “[m]ilitary purposes not connected with the use of chemical weapons and not dependent on the use of the toxic properties of chemicals as a method of warfare.

Third, WP munitions are also not “incendiary weapons” under the Protocol on Prohibitions or Restrictions on the Use of Incendiary Weapons (“Protocol III”) to the Convention on Certain Conventional Weapons (“CCW”) – both of which are binding on Russia and Ukraine (CCW: Ukraine; Russia;  Protocol III: Ukraine; Russia).  Article 1 of Protocol III defines incendiary weapons as “any weapon or munition which is primarily designed to set fire to objects or to cause burn injury to persons,” while Article 1(b)(i) clarifies that “[i]ncendiary weapons do not include: (i) [m]unitions which may have incidental incendiary effects, such as illuminants, tracers, smoke or signalling systems” (emphases added).

WP munitions escape classification and regulation under Protocol III because they are “primarily designed” as illuminants and smokescreens, and ‘only’ have incidental (though devastating) incendiary effects. States and NGOs have stressed the need to amend Protocol III to cover WP.

WP munitions are also, arguably, not expressly prohibited by customary international law as a category of weapons.

However, despite the fact that IHL does not outright prohibit WP weapons, every use of such weapons may and should be examined for its legality.  Like any other weapon, the use of WP munitions is regulated by the conventional (see Protocol I to the Geneva Conventions) and customary IHL rules, which include the principle of distinction between military objectives and civilian objects and the prohibition of targeting the latter; the prohibition of indiscriminate attacks; the prohibition of area bombardments; the requirement to take all feasible precautions in an attack to avoid and minimize incidental harm to civilians; the principle of proportionality; the prohibition of weapons indiscriminate by nature; and the prohibition of weapons of a nature to cause superfluous injury or unnecessary suffering, even against military targets.

The legality of each instance of use of WP munitions must be assessed against these fundamental principles and rules, and their breach could give rise to international responsibility for Russia, and/or criminal responsibility for war crimes by the individuals carrying out, ordering, or not preventing uses of WP munitions in contravention of the above IHL principles. Indeed, the targeting of civilians or the lodging of indiscriminate attacks and area bombardments with WP munitions could qualify as a war crime under Article 8(2)(b)(i),(ii), or (v) of the Rome Statute.

Potential Responses Under International Law To Use Of Chemical And WP Weapons By Russia In Ukraine

Responses to the alleged illegal use of chemical weapons, riot control agents, and/ or WP munitions by Russia in Ukraine could in principle seek to establish either the international responsibility of Russia as a state, or the individual criminal liability of those involved in deploying such weapons.

First, the international responsibility of Russia as a state for the illegal use of chemical weapons, riot control agents, and/ or WP munitions is unlikely to be brought before the international fora. Neither Russia nor Ukraine has accepted the compulsory jurisdiction of the International Court of Justice (“ICJ”), and thus no contentious dispute concerning possible violations of the CWC, the Geneva Conventions, their Protocols, or customary IHL norms could be brought before the ICJ through that avenue. While the CWC foresees the referral of disputes over its application to the ICJ, this would again require a special agreement between Russia and Ukraine to submit such a dispute to the Court. However, it may be possible to bring allegations of Russia’s illegal use of such weaponry before the ICJ, through a request by the UN General Assembly for an advisory opinion concerning the legality of Russia’s conduct in Ukraine.

The international responses to Syria’s use of chemical weapons may be examined as a potential precedent to apply to the situation in Ukraine.  Following the Assad regime’s 2013 horrific Ghouta attacks, western powers considered a military intervention in Syria, but this was averted through a US-Russia brokered diplomatic solution (the Joint Framework for the Elimination of Syrian Chemical Weapons), which led to Syria joining the CWC and to UN Security Council resolutions outlining Syria’s obligations to declare and destroy its chemical weapons stockpile under the oversight of joint task forces of the UN and the Organisation for the Prohibition of Chemical Weapons (“OPCW”). Syria’s stockpile declarations were seemingly incomplete and the process failed to prevent further chemical attacks, to which the US, UK, and France responded with missile strikes in 2018, reportedly aimed at sites linked to Syria’s chemical weapons program (the legal justification of which under international law has been called into question).

While announcements of “appropriate responses” to a Russian chemical attack have been made, western attacks against Russia akin to those against Syria in 2018 are unlikely.  Moreover, UN Security Council action to address allegations of chemical weapons use by Russia would be ineffective in view of Russia’s veto powers.  Also, it seems that the main steps taken toward Syria in relation to the CWC could not be taken towards Russia, which is already a CWC signatory, and has seemingly destroyed its declared chemical weapons stockpile (as verified by the OPCW in September 2017) – although it has since been accused of non-compliance, through incomplete declarations of its chemical weapons stockpile, and use of the ‘Novichok’ nerve agent in 2018 and 2020.

What could perhaps be employed to prevent a potential chemical weapons attack is the CWC’s verification apparatus. The CWC foresees procedures for State Parties to address doubts about another Party’s compliance with the Convention, including consultations, fact-finding, and the possibility to request a “challenge inspection” of another State Party’s facilities by the OPCW’s Technical Secretariat. Assuming sufficient information about Russian facilities suspected of manufacturing or storing undeclared chemical weapons stockpiles, Ukraine (or any other State Party to the CWC) could request a challenge inspection of said facilities, to locate any such stockpiles and ensure their supervised destruction. Moreover, OPCW inspections of Ukrainian facilities could be requested, to debunk potential false-flag allegations that Ukraine may have chemical weapons as a pretext for Russia to then use such weapons itself.

Second, deployment of chemical weapons, riot control agents and/or WP munitions in Ukraine and in contravention of IHL could give rise to the individual criminal liability of those involved, who could be prosecuted for war crimes before international or domestic fora.

The ICC is the international forum with jurisdiction over war crimes (among other crimes) and  can hold individuals accountable for these crimes and impose penalties, including imprisonment, fines, and forfeiture. The ICC is meant as a court of last resort, operating complementarily to domestic prosecutions. While neither Ukraine nor Russia is a State Party to the Rome Statute, Ukraine has submitted declarations accepting the ICC’s jurisdiction over alleged crimes under the Rome Statute occurring on Ukrainian territory. After a preliminary investigation of Russia’s conduct in Ukraine since 2014, and following the referral by more than 40 states of the current situation in Ukraine to the ICC, investigations, including for war crimes, were officially opened by the Prosecutor on 2 March 2022, and are carried out across Ukraine in cooperation with Ukrainian authorities to document allegations of international crimes for accountability proceedings.

Domestic prosecutions for war crimes are also possible, as long as a state has substantive criminal law provisions covering these crimes, and jurisdiction over them. In the present case, prosecutions could in principle occur before Ukrainian courts (which have territorial jurisdiction), Russian courts (which have nationality jurisdiction over the conduct of Russian nationals in Ukraine), or even before the courts of third states (through the application of universal jurisdiction).


While the international law prohibiting or considerably restricting the use of certain weaponry that Russia has been accused of deploying is generally clear, the avenues available to prosecute such complaints at the international level are less so. With discussions ongoing over the viability of establishing novel international or domestic fora to ensure accountability for Russian conduct in Ukraine, including for war crimes, until these new fora may be established the exploration of legal avenues already available to address Russian unlawful use of weaponry in Ukraine may be beneficial.

The development of these materials has been made possible through the support of the Public International Law & Policy Group.

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