The United States has accused Russia of breaching the global ban on chemical weapons by using the choking agent chloropicrin against Ukrainian soldiers and deploying riot control agents “as a method of warfare” in Ukraine.

“The use of such chemicals is not an isolated incident, and is probably driven by Russian forces’ desire to dislodge Ukrainian forces from fortified positions and achieve tactical gains on the battlefield,” the State Department said in a statement on Wednesday that also announced new sanctions against entities linked to Russia’s full-scale invasion of Ukraine.

Chloropicrin, a nearly colourless oily liquid which causes severe irritation to the eyes, skin and lungs, was used in large quantities during World War I, according to the US’s National Institute for Occupational Health and Safety.

While it continues to be used as an agricultural pesticide, its use in war is banned under the 1993 Chemical Weapons Convention (CWC).

Russia has said it no longer possesses a military chemical arsenal, but the country faces pressure for more transparency over its alleged use of toxic chemicals.

In addition to chloropicrin, Russian forces have used grenades loaded with CS and CN gasses, the Reuters news agency reported earlier this month, citing the Ukrainian military.

It added that at least 500 Ukrainian soldiers had been treated for exposure to toxic substances and one died after suffocating on tear gas.

Gyundoz Mamedov, the deputy prosecutor general in Ukraine until 2021, posted on social media on April 24 that the Russian army had used tear gas against Ukrainian forces at least 900 times over the previous six months, with more than 1,400 incidents since it began its full-scale invasion in February 2022.

While civilians can usually escape such gasses during protests, soldiers confined to trenches without gas masks are forced to either flee under enemy fire or risk suffocation.

The State Department said Moscow’s use of chloropicrin and “ongoing disregard” for the CWC “comes from the same playbook as its operations to poison Aleksei Navalny and Sergei and Yulia Skripal with Novichok nerve agents.”