An attempted assassination in Salisbury and international law – making sense of it all?

Vladimir Putin and Theresa May/Courtesy of wikimedia.

Factual Background:

Ties between Russia and the UK took a frosty turn last week after the UK accused Russia of poisoning a former Russian spy with a nerve agent near his home in the city of Salisbury, England. The use of the military-grade nerve agent known to be produced by the former Soviet Union in the 1970s and 1980s on Sergei V. Skripal, once an informant for the British intelligence services and his daughter, placed numerous bystanders at risk of exposure and harm including one police officer who is currently “seriously ill.”

This is not the first time that the UK has accused Russia of carrying out assassinations or attempted assassinations on its sovereign territory. In 2006, the UK accused Russia of  an attack using polonium-210 on Alexander Litvinenko, also a former Russian spy

What followed after the most recent attack has been public condemnation by Prime Minister Theresa May in British Parliament and a demand that Russia explain itself within a short time frame, failing which Britain would retaliate with appropriate measures. Russia shrugged off this ultimatum, and in response, Britain expelled 23 Russian diplomats from London believed to be involved in espionage. Russia responded in turn with a retaliatory expulsion of 23 British diplomats from Moscow. Moscow also said it would close the British Council in Russia and the British Consulate in St. Petersburg.

Before the UN Security Council, the US said Russia was responsible for the attack while the UK asserted that Russia was “in serious breach of the Chemical Weapons Convention through its failure to declare the novichok programme.” The EU most recently offered “unqualified solidarity” in the UK’s investigation and called on Russia to address the concerns raised by the UK and the international community.

The Kremlin in defiance, has consistently said that the UK must prove that it was responsible for the attempted assassination on British soil.

The use of force

The first statement by Prime Minister Theresa May in UK Parliament following the attempted assassination stated that the poisoning was “a direct act of the Russian state against [the UK]” and that if the Russians failed to meet the deadline for explanation, the UK would conclude that the attempted assassination was a use of force. In addition, at the UN Security Council session earlier alluded to, the British representative to the UN called the attack an unlawful use of force.

It is well known that the prohibition on the use of force is a pre-emptory (jus cogens) norm in international law, and also reflected in Art 2(4) of the UN Charter. It has been argued by Professor Marc Weller that the “killing of individuals by state agents outside of an armed conflict” is not ordinarily covered by the prohibition of the use of force, but this can be considered to be a violation of territorial sovereignty i.e. an act of intervention since this attack occurred on UK soil.

While it is possible that an act of intervention may amount to the use of force, as the International Court of Justice has stated in its Nicaragua and Armed Activities on the Territory of the Congo cases, it would seem odd that a targeted assassination can be considered a use of force. Professor Marc Weller in support of this position, points to the assassination of Kim Jong-nam on Malaysian soil in 2017, which was not classified as a use of force by Malaysia either.

In my opinion, for an act of intervention in this case to amount to the use of force, it would require an assessment of both the weapon used (military-grade chemical agent) and the gravity of force. If the UK can prove that the use of the novichok agent harmed its citizens directly (requiring a factual assessment of degree of harm and whether its citizens were targeted), and that this was an act committed by agents of Russia, then there might be a more credible claim for calling the attack a use of force. It is also worth pointing out that there was no direct attack on any state infrastructure or state organs of the UK, the occurrence of which might have made it easier to call this act a use of force

There must exist a gravity threshold under Art 2(4) of the UN Charter, which excludes “small-scale” or “targeted acts” such as this attempted assassination. Any assertion by the UK that this was a breach of the jus cogens norm prohibiting the use of force would be a deviation from standard understandings of international law. It is worth noting, as Professor Marc Weller has done in his post, that no state in the UN Security Council echoed Britain’s call that Russian actions were in violation of Art 2(4) of the UN Charter.

Much discussion by academics has also been devoted to whether the attempted assassination could constitute an armed attack under Art 51 of the UN Charter, warranting self-defense measures by the UK.

Treaty Violations

There has also been discussion devoted to the Chemical Weapons Convention, which the UK claims Russia is in violation of for either stockpiling the nerve agent or failing to control its supplies of it, leading to it landing in the wrong hands. Russia had initially wanted to resort to a mechanism in the Convention to resolve the dispute and now wants Britain to provide it with nerve agent samples. These purported treaty violations and dispute mechanism measures will become pertinent in the next part of my analysis.

Measures taken by the UK and Russia

As mentioned earlier, the UK expelled 23 Russian diplomats which the Russians responded to in turn. What is the likely legal basis for these retaliatory measures? The Vienna Convention on Diplomatic Relations 1961 and specifically Article 9, which allows a host state to declare any member of the sending State’s mission to be persona non grata.

Aside from the expulsion of diplomats and the UK stating that it would not send any ministers or royalty to the FIFA World Cup in Russia later this year, the UK has yet to take other measures against Russia. There was talk of reliance upon Article 5 of the North Atlantic Treaty, in that the UK might rely upon collective self-defense. However as mentioned earlier, this would require the UK to prove that this attempted assassination was an armed attack, similar to what is required under Article 51 of the UN Charter. But if it were to take further hardline measures such as sanctions, what would be the legal basis for such action?

Some say that the UK might rely upon countermeasures, a policy tool that has been expounded upon in the International Law Commission’s Articles on the Responsibility of States (ARSIWA) and adopted by the UN General Assembly. However, there are fairly strict conditions stipulated in Articles 49-53 of ARSIWA that cover the use of countermeasures.

A point worth noting is that the UK would not be able to rely upon countermeasures if “the internationally wrongful act has ceased.” If the attempted assassination was a singular attack, it could be said that the wrongful act has already ceased. However, the UK might rely on the continued violation by Russia of the Chemical Weapons Convention e.g. through the building of or failure to control its stockpile of the nerve agent. That adds more complexity as Russia could retort that the dispute settlement mechanism under Article XIV of the Chemical Weapons Convention precludes the use of countermeasures in light of the language contained in Article 52(3) of ARSIWA.


It has definitely been interesting to see how this dispute between Russia and the UK, which was largely political in nature, has now been framed within international law. Until all the facts have been established, the use of international law to analyze this dispute is largely speculative but has provided numerous perspectives to consider.

Rishi is a second year JD student part of the double degree (LLB-JD) program offered by Columbia Law School and King’s College London.