Cambodia lodges complaint with OPCW over alleged Thai chemical substance use

Cambodia has lodged a formal complaint with the Organisation for the Prohibition of Chemical Weapons (OPCW) over alleged use of chemical substances by Thai forces during two rounds of conflict, officials said.

According to a news report from the Cambodian outlet Kampuchea Thmey Daily, the director general of the Cambodian Mine Action Centre (CMAC), Heng Ratana, told reporters on 11 September that the complaint was submitted to the OPCW secretariat in The Hague, which oversees compliance with the Chemical Weapons Convention.

"Ratana alleged Thai forces deployed chemical substances via aircraft, drones and artillery, including 155mm and 100mm shells," Kampuchea Thmey Daily wrote, claiming that CMAC had identified 43 types of commonly used weapons during operations since July 2025, particularly after renewed fighting in December. Remnants were also said to be found near Preah Vihear Temple, rice fields and residential villages.

According to Cambodia’s Ministry of Health, 399 civilians were affected by toxic substances, while Cambodian soldiers and police officers also suffered injuries.

Both Cambodia and Thailand are parties to the CWC, which bans the use of chemical weapons. Ratana stressed the distinction between chemical weapons and chemical substances, noting their legal definitions differ under the convention.

Cambodia has previously accused Thailand of using chemical substances as a method of warfare, including in 2025. Thailand has vehemently denied the allegations and has accused Cambodia of leading a "campaign of disinformation" against the country.