The United States and the United Kingdom imposed sanctions on Russia this year over its use of the chemical weapon chloropicrin against troops in Ukraine, months before Igor Kirillov was killed in Moscow on Tuesday.

In May, the US State Department found that Russia had used chloropicrin – a counterinsurgency agent first used in World War I – against Ukrainian forces, in violation of the International Chemical Weapons Convention (CWC), to which Russia is a signatory.

Chloropicrin – an irritant that damages the eyes, skin, throat and lungs – was produced as tear gas during trench warfare in World War I, but was banned under the CWC in 1993.

In October, the UK imposed sanctions on Kirillov himself, saying he was “responsible for assisting in the deployment” of chemical weapons on Ukraine’s battlefields.

“Russian forces have openly admitted to using dangerous chemical weapons on the battlefield, with counterinsurgency agents in widespread use and multiple reports of the use of the toxic asphyxiant chloropicrin, first used on the battlefields of World War I,” said the British Foreign Office.