Thai and Cambodian troops traded gunfire and artillery shells on Friday, leaving six dead in a new clash that shattered a two-month lull in tensions along their disputed border.
Three Cambodian and three Thai soldiers were killed in the fighting. It is the latest flare-up of an ancient feud over a 900-year-old Hindu temple on disputed land claimed by both Southeast Asian nations.
Ties between the neighbouring nations have been strained since the Preah Vihear temple was granted United Nations World Heritage status in July 2008, AFP reports.
An international court ruled in 1962 that the temple belonged to Cambodia, but both claim ownership of a 4.6-square-kilometre surrounding area.
The border has never been fully demarcated, partly because it is littered with landmines left over from decades of war in Cambodia.
Each blamed the other for starting the latest clash early on Friday, which broke out near the Ta Krabei and Ta Muean Tom temples, about 100km southwest of the Preah Vihear temple.
In February, fierce fighting near the Preah Vihear temple left at least 10 people dead and prompted a UN appeal for a lasting ceasefire.
Cambodia has called for outside mediation to help end the standoff, but Thailand insists the dispute should be resolved through bilateral talks.