The dispute overshadowed a weekend summit of the 10-member Southeast Asian bloc, where Cambodian Prime Minister Hun Sen launched into a tirade against Thailand over the conflict that has left 18 dead since last month.

Thailand and Cambodia agreed in February to accept Indonesian military observers on the border but the initiative remains on ice due to Thai demands that Cambodia first pull troops out of the temple.

"An agreement had been agreed upon, (Thailand) should adhere to it, I wouldn't want to say lacking in faith... (but) they did not adhere to the agreement," Malaysian deputy foreign minister Richard Riot Jaem told reporters.

"Thailand refused and that's why the skirmish came again," said Riot, who attended the Association of Southeast Asian Nations (ASEAN) meeting where it was agreed 30 observers would be stationed on either side of the border.

"All the 10 countries, I stress, including Thailand and Cambodia, agreed to the agreement but sad to say, the agreement was brought back to the respective two countries. Cambodia accepted it, Thailand did not accept," he said.

"Before this, Cambodia was pointing at Thailand as starting the attack and Thailand said it was Cambodia who started ...so to (determine) who started the skirmish... the foreign ministers decided to assign obervers."

Some 85,000 people have been temporarily displaced in weeks of clashes over ownership of a small patch of territory surrounding an 11th-century Khmer temple. The temple itself belongs to Cambodia.

The relationship between the two countries has been strained since the 900-year-old Preah Vihear temple was granted UN World Heritage status in July 2008.

Sporadic cross-border fights have erupted since then, occasionally claiming lives, but the recent violence -- mainly at a new flashpoint about 150 km (90 miles) west of Preah Vihear -- has been the fiercest yet.

ASEAN's weakness in conflict resolution was thrown into stark relief Sunday when the leaders' final statement after the summit in Jakarta merely said the dispute "should be amicably resolved in the spirit of ASEAN solidarity".

Indonesian President Susilo Bambang Yudhoyono hosted an unscheduled meeting with the Thai and Cambodian leaders on Sunday but it failed to achieve a breakthrough in negotiations.