Russia and Ukraine have accused each other at the global chemical weapons watchdog in The Hague of using banned toxins on the battlefield, the organization said Tuesday.

The Organization for the Prohibition of Chemical Weapons (OPCW) said the accusations were "insufficiently substantiated" but added "the situation remains volatile and extremely concerning regarding the possible re-emergence of use of toxic chemicals as weapons."

Last week, the U.S. said Russia had violated the international chemical weapons ban overseen by the OPCW by deploying the choking agent chloropicrin against Ukrainian troops and using riot control agents "as a method of warfare" in Ukraine.

Russia denied the allegations.

The OPCW said it had been monitoring the situation since February 2022, when Moscow invaded Ukraine.

Under the Chemical Weapons Convention, any toxic chemical used with the purpose to cause harm or death, is considered a chemical weapon.

"It is against the Convention to use riot control agents at war on the battlefield. If used as a method of warfare, these agents are considered chemical weapons and, hence, are prohibited under the Convention," the OPCW said.