The crumbling stone temple, several hundred feet (meters) from Thailand's eastern border with Cambodia, has fueled nationalism on both sides of the disputed frontier for decades and conflict over it has sparked sporadic, brief battles in recent years. However, sustained fighting has been rare.
A one-hour clash Monday morning stopped after both sides agreed to an unofficial cease-fire. Fighting has erupted daily since Friday, leaving at least five dead.
Cambodian officials say a Thai artillery barrage Sunday collapsed part of "a wing" at the Preah Vihear temple, a U.N. World Heritage site, but Thai officials have dismissed that account as propaganda. The extent of damage was unknown because it remained too dangerous to approach the temple, Cambodian authorities said.
Both sides blame the other for instigating each day's clashes, which have shattered a series of cease-fire agreements.
Cambodian Prime Minister Hun Sen has warned that the fighting poses a threat to regional stability. He said the latest clash was sparked after Thai soldiers crossed the border in search of a slain comrade, and Cambodians opened fire to repel them. He spoke Monday during a university graduation ceremony in the capital, Phnom Penh, reiterating calls from a day earlier for U.N. intervention to halt the fighting.
"We need the United Nations to send forces here and create a buffer zone to guarantee that there is no more fighting," Hun Sen said, adding that the situation kept deteriorating and the two sides were no longer listening to each other.
Hun Sen has sent a letter to the U.N. Security Council calling for an emergency meeting to help end the fighting.
Thailand's Foreign Ministry sent its own letter to the Security Council on Monday to formally protest the "repeated and unprovoked armed attacks by Cambodian troops." In the past Thailand has ruled out foreign involvement in its dispute with Cambodia.
Cambodian government spokesman Phay Siphan said skirmishes began again early Monday after halting around midnight. There was no immediate comment from Thai authorities, but an Associated Press reporter in the area said the sound of gunfire and artillery could be heard.
Late Sunday, U.N. Secretary-General Ban Ki-moon said he was "deeply concerned" by the fighting and urged both sides "to exercise maximum restraint," his spokesperson said in a statement.
Singapore's Foreign Ministry voiced its concern in a statement Monday and called for the two neighbors to negotiate for their own sake and "the broader interests of ASEAN."
The 10-member Association of Southeast Asian Nations has long been a stable region, where the exchange of cross-border gunfire is highly unusual.
In 1962, the World Court determined that the Preah Vihear temple belongs to Cambodia. Thai nationalists dispute the ruling and have seized on it as a domestic political issue.
Built between the 9th and 11th centuries, Preah Vihear is dedicated to the Hindu diety Shiva and revered partly for having one of the most stunning locations of all the temples constructed during the Khmer empire - the most famous of which is Angkor Wat. It sits atop a 1,722-foot (525-meter) cliff in the Dangrek Mountains about 150 miles (240 kilometers) north of the Cambodian capital.
UNESCO calls the site "an outstanding masterpiece of Khmer architecture." The Khmer empire, which once encompassed parts of Thailand and Vietnam, shrank to the size of present-day Cambodia. The country was plunged into civil war, and the temple fell into disrepair.
Tensions have risen in recent days because of demonstrations in the Thai capital, Bangkok, demanding that the government oust Cambodians from the area near the temple.
At least five people have died in the border clashes that began Friday - one civilian and one soldier from Thailand and one civilian and two soldiers from Cambodia. On Sunday night, a Thai army spokesman said about 10 Thai soldiers were wounded.
Associated Press writers Thanyarat Doksone, Todd Pitman and Jocelyn Gecker also contributed to this report.