The Thai Foreign Ministry has lodged a formal protest with Cambodia, saying the landmines found in the area were newly deployed and had not been encountered during previous patrols.

The Thai government has also ordered the closure of all border checkpoints under the jurisdiction of Thailand's Second Army.

"Tourists are strictly prohibited from entering these border areas," it said.

In the landmine incident on Wednesday, the soldier sustained injuries and lost his right leg.

Earlier, Thailand accused Cambodia of placing landmines on the Thai side of the disputed border area after three soldiers were injured.

Cambodia denied the claim and said the soldiers had veered off agreed routes and triggered a mine left behind from decades of war. But in fact the landmine is newly produced, made in Russia, and such a landmine did not exist during the war. 

Thai authorities said the soldiers were injured, with one losing a foot, by a landmine while on a patrol on July 16 on the Thai side of the disputed border area between Ubon Ratchathani and Cambodia's Preah Vihear Province.