Caretaker Interior Minister Kongsak Wantana yesterday threatened legal action over the claim.

Sondhi alleged in an open letter that caretaker Prime Minister Thaksin Shinawatra had offered Cambodia half of Koh Kood, in the Gulf of Thailand, in exchange for a gas concession.

Kongsak promised an investigation and legal action if Sondhi's claim proved false, saying groundless claims damaged the country.

Meanwhile, the recipient of Sondhi's open letter, Armed Forces Supreme Commander General Ruengroj Mahasaranond, dismissed its contents. He insisted Koh Kood remained Thai territory.

The Sondhi letter to Ruengroj accused Thaksin of making an agreement with his Cambo-dian counterpart, Hun Sen, during an August 10 visit to Phnom Penh.

Ruengroj said he had looked at Royal Thai Survey Department information that showed Koh Kood's sovereignty and would furnish it to the news media.

"I insist we have never given even one square inch of Thailand to anyone. Relations between Thailand and its neighbours are good. This issue is politics," he said.

Survey Department director Lt-General Vichit Satharanond said Cambodia had never made a claim for Koh Kood and that the island's inhabitants were Thai.

However, the two countries were involved in negotiations over the maritime boundary.

Vichit said he understood that the supreme commander would be in contact with Cambodian authorities to clarify media reports of Sondhi's claim.

Department of National Parks, Wildlife and Plant Conservation director-general Damrong Pidej explained that aerial surveys proved Koh Kood was Thai territory.