Bangkok: Thai and Cambodian troops clashed with gunfire and artillery shells, leaving five dead and shattering a two-month lull in tensions along their disputed border.
It was the first serious outbreak of hostilities since fighting in February near the 900-year-old Hindu temple Preah Vihear left at least 10 dead and prompted a UN appeal for a lasting ceasefire.
Three Cambodian and two Thai soldiers were killed in Friday`s fighting near a different group of temples. Indonesia, current chair of the Association of Southeast Asian Nations (ASEAN), called for an immediate end to the violence.
The two sides blamed each other for the clash which broke out in the early morning and lasted for several hours, while thousands of villagers were evacuated on the Thai side.
"Cambodian soldiers fired with assault rifles at Thailand first and now they started to shell us with artillery and we took appropriate retaliation," Thai Defence Minister General Prawit Wongsuwon said.
"I think Cambodia wanted to take over temples on the border," he said.
Cambodia accused Thai troops of entering 0.4 kilometres (0.25 miles) into its territory.
"The Thai troops marched directly towards Cambodian troop positions stationed at Cambodia`s Ta Krabei temple and launched unprovoked attacks," said government spokesman Phay Siphan.
"This is yet another invasion by Thailand on Cambodia. We cannot accept this."
The Thai-Cambodia border has never been fully demarcated, partly because it is littered with landmines left over from decades of war in Cambodia.
Ties between the neighbours have been strained since Preah Vihear -- the most celebrated example of ancient Khmer architecture outside of Cambodia`s Angkor Wat -- was granted UN World Heritage status in July 2008.
The World Court ruled in 1962 that the temple belonged to Cambodia, but both countries claim ownership of a 4.6 square kilometre (1.8 square mile) adjacent area.
Observers say the temple dispute has been used as a rallying point to stir nationalist sentiment in Thailand and Cambodia.
The two countries agreed in late February to allow Indonesian observers in the area near Preah Vihear, but the Thai military has since said they are not welcome.
In February, UN Security Council members called for "maximum restraint" by the two countries and a permanent ceasefire -- a demand echoed by the chair of the ASEAN regional bloc on Friday.
"Indonesia, as current chair of ASEAN, strongly calls for the immediate cessation of hostilities between Cambodia and Thailand," Indonesian Foreign Minister Marty Natalegawa said in a statement.
He said he was in contact with his Thai and Cambodian counterparts, urging the two countries to "resolve their differences through peaceful means".
Cambodia has called for outside mediation to help end the standoff, but Thailand insists the dispute should be resolved through bilateral talks.
Thailand recently admitted using controversial Dual Purpose Improved Conventional Munitions during the February fighting but insisted it did not classify them as cluster munitions.
The arms are defined as cluster munitions by the global campaign group Cluster Munition Coalition (CMC), which condemned Thailand`s use of the weapons.