The US state department confirmed that Russia is using chloropicrin, a prohibited chemical deployed in the First World War.
Use of the agent on the battlefield is banned under the Chemical Weapons Convention (CWC), which Russia has signed and ratified.
The state department on Wednesday night said that the use of the gas was not an “isolated” incident.
It added that Russia has also used “riot control agents [tear gas] as a method of warfare in Ukraine, also in violation of the CWC”.
Front-line troops told The Telegraph earlier this year how their positions had been coming under near-daily attacks from small drones, mainly dropping the gas but also other chemicals.
President Joe Biden has previously warned Vladimir Putin against using chemical weapons in Ukraine. Just weeks after Russia’s invasion, Mr Biden said Putin would pay a “severe price” if he did authorise their use.
“We would respond if he uses it. The nature of the response would depend on the nature of the use,” Mr Biden said.
On Thursday, Russia denied the US accusations, calling them “baseless”. Dmitry Peskov, a Kremlin spokesman, told reporters that Moscow remained bound by its obligations under the treaty that bans chemical weapons.
“As always, such announcements are absolutely unfounded and are not supported by anything. Russia has been and remains committed to its obligations under international law in this area,” Mr Peskov said.
