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The Use of Nerve Agents in Salisbury: Why does it Matter Whether it Amounts to a Use of Force in International Law?

Over the past few days, there has been discussion of whether the attempt to murder Sergei Skripal and his daughter, in the UK, by the use of a nerve agent amounts to an unlawful use force by Russia in breach of Art. 2(4) of the United Nations Charter and customary international law (see posts by Marc Weller, Tom Ruys, and Ashley Deeks). There is agreement that if the action was attributable to Russia, it would amount to a breach of at least some obligation under international law. Marc Weller, points out that the act would amount to an unlawful intervention and a violation of the territorial sovereignty of the UK. Marko argues that these acts would also be a violation of the human rights of the individuals concerned. However, the British Prime Minister characterised the act as an unlawful use of force. What I wish to do in this post is to ask why this categorisation might matter in international law. What exactly are the implications, as a matter of law, of characterising the act as a use of force? This was an issue that was raised in the comments to Marc Weller’s post and some of the points I make below have already been made in that discussion though I expand on them. As discussed below, this characterisation might have far reaching implications in a number of areas of international law, extending beyond the possibility of self-defence, to the possibility of countermeasures, the law relating to state responsibility, the law qualification of a situation in the law of armed conflict, and international criminal law. I accept that many of the points discussed below are not clear cut, and some are even contentious. However, I think that having a catalogue of the possible consequences of the arguments relating to the use of force helps us to see more clearly what is at stake when we make these arguments.  

Use of Force, Armed Attack & Self Defence

The first point is an obvious one, saying that an act is a use of force under international law potentially opens the door to a response in self-defence. Or to put it the other way round, for something to be an armed attack which would justify a response in self-defence, it would have to be a use of force. As the International Court of Justice stated in the Nicaragua case (ICJ Reps., 1986) : “it will be necessary to distinguish the most grave forms of use of force (those constituting armed attacks) from other less grave forms.”  (para. 191, emphasis added). In this particular context, one might ask whether this is an important point given that we are unlikely to see the UK taking military action on the territory of Russia anytime soon. However, if the UK were contemplating a cyber operation in response to the alleged Russian act (as has been mooted here and here), it may well need to consider whether that cyber operation amounts to a use of force and whether that use of force can be justified on the basis of self-defence. That would depend, in the first place, on whether the use of the nerve agents was an armed attack which would in the first place require one to categorise it as a use of force. And it would also depend on a determination that a use of force in self defence is necessary to bring an attack to an end or to prevent a future imminent one, and is proportionate to the armed attack (on which see Tom Ruys’ post).

Use of Force, Countermeasures and Circumstances Precluding Wrongfulness in the Law of State Responsibility

Second, if the use of the nerve agent was a use of force by Russia then it may not be justified as a countermeasure or reprisal under the law of state responsibility (Art. 50(1) ILC Articles on State Responsibility). Now, to be clear, Russian is not even admitting to undertaking the acts and is therefore clearly not seeking to preclude the wrongfulness of the act as a countermeasure in response to a perceived UK breach of international law. However, I note this point because in arguing about the principles at stake here one ought to be attentive to the implications of the argument being made.

It is worth noting that the two points made above arguably pull in different directions. To say that a low-level use of force like the attempting killing in Salisbury is not a use of force caught by the prohibition of force is to say that it can be lawful to do it as a countermeasure. So to one can argue that those like Marc Weller who take the view that these sorts of acts are below a threshold for the use of force take a permissive approach with respect to this type of low level activity in that the view taken would allow states to do the act more often than would otherwise be the case. Permissive because it would open up the possibility that such acts may potentially be justified by circumstances precluding wrongfulness.

However, the pull in the opposite direction is this: to say, as Tom Ruys does, that the act is a use of force is to open up the possibility that self defence measures to be taken in response to it. And that position may be said to be a permissive one too with regard to the use of force.

Use of Force and Jus Cogens (and Circumstances Precluding Wrongfulness Again)

A third consequence of characterizing an act such as that in Salisbury (or any other low-level forcible act) as a use of force is that it is then arguably a beach of a jus cogens norm. This is because there is widespread acceptance that there is a jus cogens norm in the area of the prohibition of the use of force, even though there is not always agreement on how to formulate it. Whether one considers that the act in Salisbury amounted a violation of a norm of jus cogens would of course depend on what the jus cogens norm is. It may be argued that it is the prohibition of aggression that is the jus cogens norm and not the prohibition of the use of force itself. It may also then be argued that like the armed attack criterion in the law of self-defence, characterization of an act as an act of aggression requires a gravity threshold (see this piece by Antonios Tzanakopoulos and me where we note that the General Assembly Definition of Aggression, GA Res 3314 (1974) seems to include a gravity threshold in Art. 2). However, if one takes a broader view of the prohibition of aggression then any use of force which is a breach of the UN Charter, i.e a breach of the prohibition that cannot be justified under the recognized exceptions, is an act of aggression by the state concerned.

In any event, if one takes the view that the act is a use of force and a breach of a norm of jus cogens then certain consequences would follow. First circumstances precluding wrongfulness under the law of state responsibility may not pleaded as a defence to a breach of a jus cogens norm (Art 26, ILC  Articles on State Responsibility) except of course self defence and consent, which would already be ruled out for one to classify it as an act of aggression). Second if the breach is a serious one, because it is gross or systematic, there are certain consequences that follow under the law of state responsibility (Arts. 40 & 41 ILC Articles on State Resp.) – states must cooperate to bring it to an end and must not recognize the situation created by it).

Use of Force, Erga Omnes Breaches and Third Party Counter Measures

In the comments to Marc Weller’s post, Martin Dawidowicz points out a fourth consequence of determining that the act is a use of force, which is that it would be a breach of an erga omnes norm – one owed to the international community as a whole – such that… third states can invoke Russia’s responsibility. More pertinently, such a breach would then permit (n Martin’s view, and mine too) third party countermeasures as a matter of customary international law. This would mean that states other than the UK can impose countermeasures (sanctions consisting of acts that would otherwise breach international law) on Russia. If the act is a breach of a jus cogens norm, then it would automatically be a breach of an erga omnes norm. However, it could be argued that the prohibition of the use of force is itself an erga omnes norm even if that prohibition standing on its own, as distinct from the prohibition of aggression, is not a jus cogens norm.

Use of Force and International Armed Conflicts (and International Criminal Law)

A fifth consequence of charactering the act as a use of force is that it brought into effect, even if only briefly, an international armed conflict between the UK and Russia. Some, like Federica Paddeu, in the comments to Marc’s post, and Charlie Dunlap have frowned on this possibility. I have previously discussed (here, here, and here) the argument that a use of force on the territory of a state without the consent of that state brings into effect an armed conflict between the two states thus leading to the applicability of the law of international armed conflicts in relation to that conflict between the two states. I won’t repeat the argument here. However, I would like to address the concerns that have been expressed by some in relation to this argument. As Rob Lawless points out in his comment to Marc’s post, there seems to be an assumption that if there is an international armed conflict this, on its own, provides authorization to use force on the territory of another state. But it does not! We need to be clear about the different functions of the jus ad bellum and the jus in bello. The former is about whether and when a state is entitled to resort to force and the latter is about the law that applies during an armed conflict. All that the applicability of the law of armed conflict does is to trigger for participants in an armed conflict, the prohibitions, protections and (in an international armed conflict) permissions that might exist in that body of law. Nothing in the law of armed conflict excuses a violation of the prohibition of the use of force on the territory of another state. Only the exceptions to the prohibition that are contained in the Charter would excuse such a violation.  Thus, the only thing that authorizes the use of force in another state is the jus ad bellum. For the UK to use force against Russia, it would need to show that its actions are being conducted in self defence (since it would be impossible for the Security Council to authorize such an action).

I take the point that this legal nuance may be lost on the public. But it is one that lawyers have an obligation to explain to policy makers.

As Ryan Goodman and Alex Whiting have pointed out, if there was an armed conflict between Russia and the UK then the possibility of treating the attempted killings as war crimes arises. This has implications not only for the ICC as the suggest but also has implications for domestic prosecutions whether in the UK or elsewhere of persons who are alleged to be responsible for the acts. Assuming these persons are Russian officials who were acting in their official capacity, the question whether they would have immunity ratione materiae from prosecution would arise. If the acts are war crimes then there is a strong argument that there is no immunity ratione materiae (see this article by Sangeeta Shah and me  and see also the International Law Commission’s  Draft Art. 7 on the Immunity of Officials from Foreign Criminal Jurisdiction adopted in 2017)


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