The Organisation for the Prohibition of Chemical Weapons (OPCW) has once again detected traces of tear gas on the frontline in Ukraine’s Dnipropetrovsk region, the global chemical weapons watchdog confirmed on Friday.

Following a request from Ukraine, an OPCW team was deployed to investigate incidents in the region. The agency collected soil samples and grenade shell fragments from three sites in October, which tested positive for tear gas. A similar finding had been reported in November.

Under the Chemical Weapons Convention, the use of riot control agents such as tear gas as a method of warfare is strictly prohibited. While the OPCW team was not authorized to determine responsibility, Ukraine and the United States have accused Russia of using tear gas to clear trenches.

Tear gas, though not lethal, causes temporary irritation to the eyes and respiratory system. The latest findings add to ongoing concerns about the use of chemical agents in the conflict.