The United States has accused Russia of using the banned choking gas Chloropicrin to drive out Ukrainian troops in the eastern European country. The use of Chloropicrin is prohibited by the 1993 Chemical Weapons Convention, which Russia signed. Moscow has denied the allegations. The gas can cause tearing and burning sensations in the eyes and skin, affect the lungs, and cause nausea and vomiting. US officials have alleged that Russia has stepped up the use of “riot control agents” or tear gas during its “military operation” in Ukraine.