Cambodian and Thai troops clashed briefly Monday for a fourth straight day, Phnom Penh said, as UN chief Ban Ki-moon called for "maximum restraint" in a border dispute that has claimed six lives.
The latest flare-up erupted during an operation by Thai soldiers to recover casualties from Sunday's heavy fighting, according to Cambodia, which accused Thailand of damaging an 11th-century temple at the centre of the hostilities.
Cambodia said one of its soldiers was killed overnight and accused Thailand of wanting to occupy the disputed 4.6-square-kilometre area around the Preah Vihear temple.
Thailand, however, played down the latest skirmish, with a military source near the border describing it as a "misunderstanding".
The renewed clashes, which were reported to have injured 13 Thai soldiers on Sunday night, shattered a brief ceasefire agreed on Saturday after the worst fighting between the two neighbours in years.
In New York, Ban's office said the UN chief was "deeply concerned" about the standoff.
"The secretary-general appeals to both sides to put in place an effective arrangement for cessation of hostilities and to exercise maximum restraint," it said.
Cambodia said Sunday that the ancient Preah Vihear temple, which is surrounded by disputed territory, was damaged by Thai artillery fire, with one wing of the building "collapsed".
Sombo Manara, a history professor at the Royal University of Phnom Penh, said long-standing disagreement over the countries' border was behind the dispute.
"I don't think that the conflict will end without intervention from a third party and clear demarcation (of the border) between the two countries," he said.
Thousands of people living in villages on both sides of the frontier have fled their homes since the clashes erupted on Friday.
About 15,000 people spent the night at 38 temporary shelters and 23 schools near the border were told to close from Monday to Wednesday, according to Somsak Suwansujarit, governor of Thailand's eastern border province Si Sa Ket.
It is unclear exactly what triggered the latest violence, but diplomatic frictions have grown since late December when seven Thais, including one lawmaker, were arrested by Cambodia near the border for illegal entry.
Two of them were sentenced to lengthy jail terms for spying, in a case that has caused outrage among nationalist Thais, who have held protests in Bangkok calling for Prime Minister Abhisit Vejjajiva to resign.
Cambodian Prime Minister Hun Sen has urged the United Nations Security Council to hold an urgent meeting about what he described as "Thailand's aggression", warning that regional stability was at risk.
He also said he would welcome intervention from the Association of Southeast Asian Nations (ASEAN), to which both countries belong.
His son Hun Manet, who was recently promoted to a two-star general at the age of 33, is involved in border strategy and negotiations with his Thai counterparts to ease tensions, the premier said.
Ties between the neighbours have been strained since Preah Vihear was granted UN World Heritage status in July 2008. Thailand and Cambodia have each accused the other of starting the ongoing clashes.
"Thailand does not invade any country. We protect our sovereignty," Thai Deputy Prime Minister Suthep Thaugsuban told reporters.
"The army has reaffirmed that retaliation was conducted carefully and avoided the temple," he said.
The World Court ruled in 1962 that Preah Vihear itself belonged to Cambodia, although its main entrance lies in Thailand.
The foreign minister of Indonesia, the current chair of the Association of Southeast Asian Nations, was expected in Cambodia on Monday but Thailand has dismissed intervention by the regional bloc as "unnecessary".