BAN NONGKANA, Thailand (Reuters) - Thai and Cambodian troops clashed for a third straight day on Sunday over their disputed border, with gunfire and explosions echoing through mountainous jungle for several hours despite a call for a ceasefire by UN Secretary-General Ban Ki-moon. The fighting near two disputed 12th-century Hindu temples killed at least 10 people on Friday and Saturday, and follows a four-day confrontation in February that claimed 11 lives, making this year's standoff the bloodiest in nearly two decades and raising questions over what's behind it. Cambodia's Defence Ministry accused Thailand of shelling civilian villages, a day after saying Thai soldiers fired cluster munitions - anti-personnel weapons banned by many countries - along with shells "loaded with poisonous gas." The Thai government said the allegations were "groundless." No one was reported killed on Sunday, though each side said at least one soldier was wounded. The official toll since Friday is four Thai soldiers killed and 25 wounded, and six Cambodians killed and 17 wounded. "The situation is still under control at the moment. We can handle it," said Thai Army Lieutenant-General Thawatchai Samutsakorn, adding that he believed Cambodia's casualties outnumbered those in Thailand. The UN's Ban called for maximum restraint, "serious dialogue" and an "effective and verifiable" solution to a conflict that he in February urged the Association of South East Asian Nations (ASEAN) to help settle. Marty Natalegawa, foreign minister of Indonesia and ASEAN chair, will meet with the Thai and Cambodian foreign ministers on Monday. Thailand and Cambodia agreed on February 22 to allow unarmed military observers from Indonesia to be posted along their border as part of a ceasefire deal. But that arrangement has yet to be put in place. Thailand said international observers were not required, insisting the dispute can resolved bilaterally. "We must not fall into Cambodia's trap in trying to spread a picture of conflict, or say the conflict is unsolvable through bilateral talks. We will definitely not let that happen," Thai Prime Minister Abhisit Vejjajiva said in his weekly televised address on Sunday. "It's the duty of all Thai people to defend our sovereignty," he said. As usual in Thai-Cambodian disputes, each side accused the other of firing first, but witnesses said the heaviest artillery appeared to be fired from the Thai side. Regular intervals of Thai rocket-fire could be heard by Reuters' journalists. The confrontation comes just a week before Abhisit is expected to dissolve parliament, paving the way for a close election expected by July. Some analysts say the government may be trying to flex its military muscle to score political points. Others say hawkish Thai generals and their ultra-nationalist allies may be trying to create a pretext for a coup to cancel the elections. Cambodia's government may also be trying to stir nationalist fervor by starting a conflict to show its army can stand up to its historic rival, or there may have been a simple breakdown in communications at a time of strained relations. There has been little official explanation for the fighting. Those caught up in the violence say they fear ties with their cross-border neighbors, many of whom are blood relatives, may never be the same. "They are like our brothers and sisters. We have no reason to fight. We don't know what happened. We don't know why it happened, but we're all scared," said Wanchai Chaensit, 48, a farmer who fled his village 3 km (1.9 miles) from the fighting. Some were loading pick-up trucks with family and pets and fleeing rustic villages dotted with Thai flags denoting Thailand's claim to sovereignty of the area. Others packed into newly dug bunkers in the jungles around the Ta Moan and Ta Krabey temples, about 150 km (93 miles) west of the 900-year-old Preah Vihear temple, scene of intense fighting in February. Thousands sheltered in evacuation camps. Sovereignty over the ancient, stone-walled Hindu temples - Preah Vihear, Ta Moan and Ta Krabey - and the jungle of the Dangrek Mountains surrounding them has been in dispute since the withdrawal of the French from Cambodia in the 1950s. Thailand says the temples perched on an escarpment in land mine-infested terrain are in its Surin province according to a 1947 map. Cambodia says they are its territory. Before Friday, Cambodian and Thai soldiers jointly patrolled the area largely without incident. Villagers on both sides, many of whom share the same ethnic makeup, mingle and trade each day. The two countries have been at loggerheads since July 2008, when Preah Vihear, which is under Cambodia's jurisdiction, was granted UNESCO World Heritage status, which Thailand opposed on the grounds that the land around it had never been demarcated.