Cambodia accused Thailand Monday of damaging ancient jungle temples at the centre of their bloodiest fighting since a bitter border dispute flared up almost three years ago. Twelve soldiers have died and tens of thousands of villagers on both sides fled the artillery shelling, which shattered an informal ceasefire that had held since February when the UN Security Council called for a permanent truce. The fighting resumed again on Monday afternoon with several shells fired, both sides said, as usual blaming each other for the violence. The clashes began on Friday near two groups of contested temples -- named Ta Kwai and Ta Muen in Thai or Ta Krabei and Ta Moan in Khmer -- deep inside the jungle away from the main tourist trail. The Cambodian defence ministry said in a statement that the Thai attacks had caused damage to the ruins, without giving further details. \"We do not know the extent of the damage to the temples yet,\" said ministry of defence spokesman Chhum Socheat. Seven Cambodian and five Thai troops have died in the violence. Another Cambodian soldier has been missing since 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. Others, like 47-year-old Suwech Yodsri, stayed behind to guard their properties, despite the danger from shells falling in the area. \"I\'m scared to be here but I have to be here to protect our village from looting,\" he told AFP in 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. Residents said that since Friday about 10 shells had fallen in the village, which was almost deserted. A man carrying a rifle patrolled the empty streets on his motorcycle. It is the first serious outbreak of hostilities since February when 10 people were killed in clashes near the 900-year-old disputed Preah Vihear temple about 150 kilometres (90 miles) away from the latest flashpoint. The fighting comes at a sensitive political time for Thailand, with Prime Minister Abhisit Vejjajiva preparing to dissolve the lower house of parliament soon for elections he has said will be held by early July. Abhisit said he hoped the border situation would improve before he meets his Cambodian counterpart Hun Sen at a regional summit on May 7-8. \"We don\'t want it to escalate. We want to return to normal soon because it affects people in both countries,\" he said. Ties between the two countries have been strained since Preah Vihear 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) surrounding area. Cambodia has accused Thailand of using spy planes and poisonous gas in the recent fighting -- claims that Bangkok has strongly denied. It also accused Thailand of firing more than 300 artillery shells on civilian villages. Thailand recently admitted using controversial munitions designed to burst into bomblets during the February fighting. Indonesia, which holds the rotating chairmanship of the Association of Southeast Asian Nations regional bloc, has called for an immediate end to the violence. The neighbours agreed in late February to allow Indonesian observers near Preah Vihear, but the Thai military has since said they are not welcome and the monitors have not been deployed. Indonesian Foreign Minister Marty Natalegawa had been expected to travel to both countries on Monday for talks on the conflict, but the visit was postponed.