Caretaker Prime Minister Thaksin Shinawatra made the request during a whistle-stop visit to Burma on Wednesday.

Thaksin met with Burma's top leader Senior General Than Shwe. He asked that Thailand's biggest energy company, PTT Plc, be permitted exclusive rights to a natural-gas field in the Bay of Bengal.

Several Cabinet ministers and the Army commander-in-chief accompanied the PM, who flew in for a hastily organised one-on-one with the reclusive junta leader.

The rushed and unclear circumstances of the meeting prompted a call from opposition leader Abhisit Vejjajiva for Thaksin to come clean about the real reasons for the trip.

The rare visit caught many people by surprise, including ministers and the Army chief, who all had to cancel other engagements to accompany the premier.

Thaksin became the first foreign leader to visit Burma's new administrative capital of Pyinmana, six hours north of Rangoon.

Thaksin dodged questions about his private meeting with Than Shwe. The PM simply told reporters yesterday he had asked the Burmese leaders to release

pro-democracy leader Aung San Suu Kyi.

He refused to elaborate, saying it would not be "proper" to disclose his discussions with the junta chief.

"All you need to know is that we conveyed our points of concern as their neighbour and said it would benefit regional politics," he said.

Viset told reporters yesterday that Thaksin tried to persuade Burma to give an exclusive gas concession to PTT Exploration and Production Plc (PTTEP). But he did not say if the premier's request was successful. The natural-gas sites are in the A-1 oilfield in the Bay of Bengal.

Viset said if Thailand received the concession, it should boost energy security in the long term. PTTEP had already secured a concession to explore the M-9 oilfield in Burma and preliminary surveys showed there was substantial gas and oil reserves. Thailand pipes about one billion cubic feet of gas per day from Burma's offshore reserves in the Andaman Sea.

Energy-hungry Thailand is also set to fund construction of controversial dams in Burma's northeast, on the Salween River.

Foreign Minister Kantathi Suphamongkhon yesterday downplayed Thaksin's surprise trip, describing it as "normal".

Kantathi said he conveyed Thailand's desire to see Suu Kyi and other political prisoners released "soon" to his Burma counterpart Nyan Win. He said the junta agreed to take "Thailand's concerns into consideration. We want to see concrete progress in Burma towards democracy," he said.

The fact that this "sensitive topic" was discussed was a "positive development", Kantathi said.