A Thai soldier was seriously injured by a landmine near the Cambodian border, just days after the two countries agreed to a ceasefire following last month’s deadly clashes.

Royal Thai Army spokesperson Maj. Gen. Winthai Suvaree said the sergeant was patrolling about one kilometer from the Ta Moan Thom temple in Surin province when he stepped on an anti-personnel mine, severely injuring his left ankle. He is being treated in hospital.

Tuesday’s landmine incident was the fourth in roughly a month and the second since the ceasefire.

“Cambodia continues to covertly plant landmines while the Thai army has consistently adhered to peaceful approaches and has not been the initiating party,” Suvaree said in a statement. 

The statement added that if such violations continue, Thailand might “exercise the right of self-defence under international law principles to resolve situations that cause Thailand to continuously lose personnel due to violations of ceasefire agreements and sovereignty encroachments by Cambodian military forces.”

Meanwhile, Cambodia denied Thailand’s accusations and said it had no involvement in the incident.

“Cambodia has absolutely not and will not use or plant any new landmine,” the Cambodian Ministry of National Defence said in a social media post. “Cambodia is a proud state party to the Anti-Personnel Mine Ban Convention, which it ratified in 1999, and has been recognized by the international community for its demining efforts at home and abroad.”

Cambodia added that it has repeatedly reminded Thailand that border areas still contain explosives left over from past conflicts. It urged all parties to avoid making public conclusions before the facts are confirmed “to avoid misunderstanding that could escalate tension and confrontation.”