The U.S. State Department said on May 1 that Russian forces have used the chemical agent chloropicrin in Ukraine.
The announcement was part of a larger statement about the introduction of new U.S. sanctions against more than 280 individuals and entities.
Ukrainian military officials have previously accused Russia of using chloropicrin and other chemical weapons.
Chloropicrin is often used as an herbicide. According to the U.S. Centers for Disease Control (CDC), exposure to its vapors can cause severe irritation to the skin, eyes, and, if inhaled, internal organs.
Although less lethal than other chemical weapons, it was used extensively in World War I before the 1925 Geneva Protocol prohibited the use of chemical and biological weapons in war.
Ukrainian military officials have also said that Russia is deploying tear gas and other riot control chemicals, which are banned under the 1997 Chemical Weapons Convention (CWC), of which Russia is a signatory.
"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.
The State Department also announced sanctions against three Russian government entities and four Russian companies in connection with the usage of such chemical weapons.
Separately, the U.S. Treasury Department announced it was sanctioning around 200 companies and individuals, including Chinese businesses, for supporting Russia's war machine and its chemical weapons program.
Read also: The Counteroffensive: Russia’s rising chemical weapons use in Ukraine