BANGKOK - THAILAND'S cabinet violated the constitution by endorsing a deal backing Cambodia's bid for the UN cultural agency to declare an 11th century temple a World Heritage Site, a court ruled on Tuesday.

Thailand and Cambodia have disputed the border around the mountaintop Preah Vihear temple for decades.

The Constitutional Court ruled that the cabinet should have sought parliamentary approval for the joint communique backing Cambodia's bid for Unesco recognition, the court's secretary general Paiboon Varahapaitoon said.

'The judges ruled 8 to 1 that the joint communique was an international agreement that requires approval from parliament,' he said.

The ruling poses a new political threat to the five-month-old government of Prime Minister Samak Sundaravej. The parliamentary opposition can use the court verdict to launch impeachment proceedings against the entire cabinet.

Unesco late on Monday added the Preah Vihear temple to its list of protected sites, saying the decision had no bearing on the border dispute.

The agency also left the door open to future talks that would expand the protected area to include parts of the temple grounds on the Thai side of the border.

The ruins of the Hindu temple are the most important example of ancient Khmer architecture outside of Cambodia's famed Angkor Wat.

The World Court ruled in 1962 that the Hindu temple belonged to Cambodia, although the main entrance lies at the foot of a mountain in Thailand. The exact boundary through the surrounding grounds remains in dispute.

The controversy appeared resolved last month after Foreign Minister Noppadon Pattama signed a joint communique supporting Cambodia's bid for UNESCO recognition.

But the deal sparked a political controversy in Thailand, and Cambodia closed the temple two weeks ago after 100 Thai protesters tried to march there.

Mr Noppadon has come under heavy fire for signing the deal, and the issue became a major subject of debate during a no confidence vote last month, which Mr Samak survived easily. -- AFP