|Thousands of civilians have fled the border area, seeking refuge from the three days of fighting [Reuters]
The death toll from three days of heavy fighting between Thai and Cambodian troops over a disputed border area has climbed to 12.
Officials on Monday said one soldier had been killed on each side following an exchange of fire in the jungle frontier late on Sunday.
Cambodia also accused Thailand of damaging two ancient temples during the latest clashes, while Thailand accused the Cambodian army of firing artillery shells that did not make it across the border.
Fighting appeared to have resumed on Monday afternoon with several shells fired, following a brief lull in the violence after days of cross-border shelling.
Thailand's foreign minister called for one-on-one talks with Cambodia, a renewed push that came after the cancellation of talks with a top regional envoy.
Indonesian foreign minister Marty Natalegawa had been scheduled to hold talks in Thailand and Cambodia on Monday but his trip was cancelled, government officials from both countries said.
Natalegawa had brokered a UN-backed peace deal in February that would have posted unarmed military observers from Indonesia along the border, but the Thai military has said they are not welcome and the deal has yet to be put in place.
Panitan Wattanayagorn, a Thai government spokesman, said Natalegawa's visit was cancelled because Thailand and Cambodia had not yet settled on terms for the Indonesian observers.
Cambodia has asked for outside mediation to help end the standoff, but Thailand has resisted third-party intervention. However, Kasit Piromya, the Thai foreign minister, declined on Monday to rule them out when
speaking to reporters at an evacuation camp.
"It's not something we are opposed to. This is a sensitive issue," he said in a briefing about 30km from the scene of recent fighting.
Both countries have blamed each other for sparking the violence, which is the first serious outbreak of fighting since February, when 10 people were killed in clashes near the 900-year-old Hindu temple Preah Vihear.
Seven Cambodian and five Thai troops have been killed and thousands of civilians have fled the area since the latest clashes began on Friday.
About 20,000 civilians have sought refuge in 16 camps on the Thai side of the border while about 17,000 have been evacuated from Cambodian villages.
Some, like 47-year-old Suwech Yodsri, stayed behind to guard their properties, despite the danger of violence.
"I'm scared to be here but I have to be here to protect our village from looting," he told the AFP news agency from the Thai village of Nong Kanna in Surin Province, about five kilometres from the border.
"I believe political conflicts are to blame. Innocent people are just being used as a political tool," he added.
Calls for restraint
Ban Ki-moon, the UN secretary-general, has called on the neighbours to "exercise maximum restraint" and has urged them to resolve the issue through "serious dialogue" rather than military means.
He also urged the two neighbours to take immediate measures for an effective and verifiable ceasefire.
Indonesia, which holds the rotating chairmanship of the Association of Southeast Asian Nations regional bloc, has called for an immediate end to the violence. Vietnam urged "maximum restraint".
Ties between the neighbours have been strained since Preah Vihear -- the most celebrated example of ancient Khmer architecture outside Cambodia's Angkor -- was granted UN World Heritage status in July 2008.
The International Court of Justice ruled in 1962 that the temple belonged to Cambodia, but both countries claim ownership of a 4.6 square km surrounding area.