Since last summer dozens have been killed in waves of conflict along the nations’ jungle-bound border, disputed for more than a century since its demarcation in the French colonial era.

More than a million civilians were displaced along the 800-kilometre (500-mile) frontier at the height of the fighting in July and December, before a tentative ceasefire took effect.

“One soldier has been critically wounded and lost his right leg after stepping on a landmine,” the Thai army said in a statement, adding the incident took place around dawn in the border province of Surin.

Thailand and Cambodia have repeatedly accused each other of violating successive truces with cross-border gun and mortar fire, while Bangkok has alleged Phnomh Penh’s soldiers have laid fresh landmines on contested soil.

However the Thai military said a “preliminary examination” of Friday’s blast “indicates that the landmine was buried deep in clay and covered with leaves, suggesting it was not newly laid”.

Cambodia’s border is still littered with unexploded ordinance dating back to separate conflicts decades ago.

Under the December truce, Cambodia and Thailand pledged to cease fire, freeze troop movements and cooperate on demining efforts along the frontier.