PHNOM PENH, Cambodia >> Thai and Cambodian forces battled for a fourth straight day along their disputed border Monday, as Cambodia accused its neighbor of damaging two ancient temples in weekend clashes.

Southeast Asian diplomats are struggling to end the repeated deadly flare-ups, but Thailand’s prime minister appeared to reject outside help Monday, saying the two countries have to resolve the dispute alone.

The fighting on land around temples and several other crumbling stone monuments is rooted in a long-running dispute over where the border should be drawn and has fueled profound nationalistic fervor in both countries for decades.

Field commanders on both sides reported heavy exchanges of fire after nightfall Monday around Ta Krabey temple. Cambodian Col. Suos Sothea said from the front that both sides had fired artillery, mortars and rifles.

Thai army spokesman Col. Sansern Kaewkamnerd confirmed that account, saying "we could not stay still and allow them to attack. We had to counter responsively."

Both sides have accused each other of starting the latest battles, which by Sunday had killed at least 12 soldiers on both sides and forced 30,000 people in Thailand and another 17,000 in Cambodia to flee.

While a wider war seems unlikely, several cease-fires have failed to prevent new border bloodshed. U.N. Secretary-General Ban Ki-moon has called for a cease-fire, but the prospects for peace appear shaky.

Most of the recent fighting has taken place around the 1,000-year-old Ta Moan and Ta Krabey temples, which are on territory claimed by both countries. The temples date back to the Khmer empire that once ruled over much of both Cambodia and Thailand.

Cambodian government spokesman Phay Siphan said the two temple complexes, caught in crossfire over the weekend, had been hit by bullets and shells, but there was no word on how bad the damage was. Thai authorities had no immediate comment on the allegation.

This month’s renewed fighting comes as Thailand prepares for general elections expected by early July. The Thai army, which staged a coup in 2006 and continues to hold influence in domestic politics, has effectively vetoed a plan to station Indonesian observers to monitor the border situation.

Indonesian Foreign Minister Marty Natalegawa was in "intense" talks with both sides to secure an end to the conflict in his role as current chair of the Association of Southeast Asian Nations, Foreign Ministry official Hamzah Thayeb said.

Natalegawa postponed a scheduled trip Monday to Cambodia, Thayeb said, as Indonesia continued to push to send military observers to the region — a move that Thailand has so far vehemently rejected. The trip’s cancellation cast doubt on hopes the simmering dispute might be resolved quickly.

Thai Prime Minister Abhisit Vejjajiva said the border issue must be solved by Thailand and Cambodia themselves, saying third-party involvement might make it "more complicated"

"There is no need for a third country to intervene," said Abhisit. "Eventually there has to be a talk between Thailand and Cambodia."

Abhisit said he would meet Cambodian Prime Minister Hun Sen during a two-day ASEAN summit due in Indonesia on May 7.

The conflict involves small swaths of land along the border that have been disputed for more than half a century. Fierce clashes have broken out several times since 2008, when Cambodia’s 11th-century Preah Vihear temple was given U.N. World Heritage status over Thailand’s objections.

In recent years, political groups on both sides have accused their opponents of using the skirmishes to stir nationalistic fever and further their own domestic political agendas.

Cambodian Prime Minister Hun Sen has harnessed the dispute in the past to build political support. And during the last round of fighting in February, Thai nationalists launched a sit-in outside government buildings in part to demand the country take a tough stand against Cambodia. The group is widely seen as playing the patriotism card in a bid to exercise more influence over politics at home.

The current round of clashes are the first since February, when eight soldiers and civilians were killed near the more well known Preah Vihear, which suffered minor damage from exploding artillery and mortar shells that knocked small chunks out of a few of its walls.

The latest fighting over the last several days broke out about 100 miles (160 kilometers) west of Preah Vihear. After easing earlier Sunday, fighting resumed later that night, both sides said, raising the toll from 10 to 12.

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Doksone reported from Bangkok; Niniek Karmini in Jakarta, Indonesia, contributed to this report.