Thai military trucks with soldiers are driven to the Thai-Cambodia border for reinforcement in this still image taken from video April 22, 2011 (Reuters/Reuters TV)

THAI and Cambodian soldiers fought with rocket-propelled grenades and guns on their contentious border on Friday in a dawn clash that left at least five troops dead in the first major flare-up since a shaky ceasefire in February.

Both sides evacuated villagers and accused each other of firing first in the thick jungle around Ta Moan and Ta Krabey temples, about 150 kilometres southwest of the 900-year-old Preah Vihear temple, which saw a deadly stand-off in February.

Council of Ministers spokesman Phay Siphan said the fighting broke out after Thai troops fired on their Cambodian counterparts around 6 AM on Friday near Ta Krabey temple, about 15 kilometres from Ta Moan temple in Oddar Meanchey province.

The government was still tallying the final damage on Friday, but preliminary reports said three Cambodian soldiers were killed, he added. Shelling and artillery fire were continuing intermittently as of Friday afternoon.

“We did not start this fight,” Phay Siphan said. “We cannot accept this act. It is not what Cambodia wants, and it affects our Ta Krabey temple.”

“They are trying to take advantage by fighting and encroaching on Cambodia. They have breached the principles of our agreement in Indonesia,” Phay Siphan added, referring to talks between the two sides following their clashes in February in which they agreed to accept Indonesian military observers to preserve the fragile ceasefire at the border.

These observers have yet to arrive due to Thailand’s hesitance to grant them final approval.

Defence Ministry spokesman Chhum Socheat said Thai shells had landed more than 20 kilometres inside Cambodian territory. Ceasefire talks between the two sides had not yet begun as of yesterday afternoon, he added.

Thailand, claimed, meanwhile, that Cambodia had started the fight.

“Cambodia started attacking our temporary base with artillery fire and we responded to defend ourselves,” said Lt. General Thawatchai Samutsakorn of the Thai army.

“Tensions have eased for now, but both sides are holding position.”

Two Thai paramilitary rangers were killed and seven wounded, said Thai armyspokeswoman Sirichan Ngathong, claiming that fighting began after Cambodian troops altered a bunker in the area in violation of a ceasefire pact. The Bangkok Post, meanwhile, reported Friday afternoon that four Thai troops had been killed and eight wounded.

"When warned, Cambodian troops stepped closer and started firing," Sirichan said.

As a precaution, the Thai government evacuated about 7,500 villagers from the area. Cambodian authorities evacuated about 200 families, according to local officials.

The fighting is the most severe since three Thais and eight Cambodians were killed and dozens of people wounded over Feb. 4-7 in the bloodiest fighting in nearly two decades.

As part of a ceasefire deal, Thailand and Cambodia agreed on Feb. 22 to allow unarmed military observers from Indonesia to be posted along their border.

But that arrangement -- brokered by a meeting of Association for South East Asian Nations (ASEAN) foreign ministers in Jakarta -- has yet to be put in place. Thailand's military said international observers were not required.

Chhay Mao, a major in the Cambodian army stationed at Preah Vihear temple, said the fighting had not spread to the ancient clifftop temple. “It is quiet at Preah Vihear now but we are ready at our side,” he said.

Indonesian Foreign Minister Marty Natalegawa, whose country currently holds the chair of ASEAN, urged both sides to halt hostilities.

“I call for both sides to resolve their differences through peaceful means. The use of force has no place in relations among ASEAN member countries," he said, according to the Bangkok Post.

The Singaporean Ministry of Foreign Affairs issued a statement Friday saying that it supported the mediation efforts by Indonesia’s Natalegawa, who contacted both sides following the clashes.

“Indonesia, as ASEAN Chair, has been actively facilitating dialogue between the two countries to resolve their differences peacefully,” the statement read. “This is important for the long term relationship of Cambodia and Thailand, as well as in the broader interests of ASEAN.”

In a letter to the United Nations Security Council dated Friday, Cambodian Foreign Minister Hor Namhong called the clashes "a fresh act of aggression" by Thailand.

“The most recent aggression against Cambodia also confirms the reason behind Thailand's insistence on resolving the conflict ‘bilaterally’, which is a pretext for using its larger and materially more sophisticated armed forces against Cambodia,” Hor Namhong wrote.

Thailand and Cambodia have been locked in a standoff since July 2008, when UNESCO enshrined Preah Vihear as a World Heritage site for Cambodia over Thai objections.

But the reasons behind this year's deadly skirmishes are murky.

Some analysts say hawkish Thai generals and their ultra-nationalist allies, who wear the Thai king's colour of yellow at protests, may be trying to create a crisis that would bring down Thailand's government or create a pretext to stage a coup and cancel elections expected in June or July.

Others say it may be a simple breakdown in communication at a time of strained relations.