The US alleged that Russia has been using chloropicrin, a choking agent, against Ukrainian forces.
Such a method of warfare violates international law, specifically the Chemical Weapons Convention (CWC), and officials claim that this was not an isolated incident.
They also said Russia used "riot control agents," also known as tear gas.
States who have signed the CWC agree to the "prohibit[ion] [of] the development, production, acquisition, stockpiling, retention, transfer or use of chemical weapons by States Parties". Russia and around 193 states have accepted these provisions.
Press secretary Dmitry Peskov maintained that Russia adhered to the CWC's stipulations, and dismissed the accusations as "baseless".
However, the Ukrainian armed forces released a statement on social media, saying they have recorded upwards of a thousand occassions where they endured confrontations with “tear gas munitions equipped with toxic chemicals that are prohibited for warfare."
There have also been testimonies from Ukrainian soldiers.
News outlet Reuters reported that more than 500 Ukrainian soldiers required medical attention after being subjected to noxious gases. One died, suffocated by tear gas.
President Joe Biden had warned President Vladimir Putin that he would pay "severe[ly]" if he were to breach the convention.
Chloropicrin was commonly used during the first World War. It is an oily substance with effects that include irritation of the lungs, eyes, and skin, nausea, vomiting, and diarrhea which may last for weeks.
Its use as a military weapon has been banned, but is still used in agriculture.
