Shortly after taking office, General Surayud Chulanont insisted that he would "act on my own conscience" and work to heal political divisions after the months of turmoil that led to the September 19 ouster of Thaksin Shinawatra.

The junta says that Surayud will only lead the country for one year, until elections promised for October 2007.

But under the constitution unveiled earlier Sunday, the junta will be able to sack him and to play a powerful role in reshaping Thai politics.

Asked why he had decided to accept the premiership, Surayud told reporters he had to take the job "because of the necessity to address the country's problems."

"I will act on my own conscience as prime minister," Surayud added.

Even though Surayud has a reputation as a military reformer and a man of integrity, analysts warned that his appointment and the military-imposed constitution signal the junta has no intention of letting go of power any time soon.

"This constitution is a step backward, away from democracy," warned Prinya Thaewanarumitkul, a political science professor at Thammasat University.

"If the new constitution does not look good, the people will hold the (military) council responsible."

The junta has insisted that they staged the coup in support of democracy, which they say had been undermined by endemic corruption during Thaksin's five years in office.

But now the generals will have to overcome at least the perception that the premier's office has become little more than an extension of the military.

That concern has already been voiced by the United States, Thailand's top trade partner and a close ally, which last week suspended 24 million dollars in military aid in protest at the coup.

"He (Surayud) is well known for being honest, politically neutral, and consistent, which makes Surayud well-suited for the position," said Sukhum Chaleysub of Rajabhat Suan Dusit University.

"However, now I think we need to focus more on the cabinet. If people with experience are in the cabinet, rather than people in uniform, that will draw less criticism to the government," he said.

Surayud, who was sworn in Sunday afternoon in a brief ceremony at Government House, is a career soldier who won respect for professionalising the armed forces after he became army chief in 1998.

He had previously spoken out against the military playing a role in Thai politics after troops under his command shot dead more than 50 pro-democracy protesters in 1992.

Surayud later clashed with Thaksin and was sidelined in a less powerful post, before he retired in 2003.

He then joined the Privy Council, the king's inner circle of advisors, but had to quit that post in order to become prime minister.

His powers as premier will be sharply checked by the junta under the interim constitution that the king approved earlier Sunday.

The charter formalizes the junta's role in government by renaming them the Council for National Security, a body which will oversee the nation's defence and which has the power to sack the prime minister.

The military will also appoint all 250 members of the new parliament, and will approve all members of a new assembly tasked with writing a permanent constitution for Thailand before the promised elections.

The charter bars political parties from participating in the drafting of the constitution and grants the military complete amnesty for the coup.

Thaksin's ouster came after months of political upheaval following his family's tax-free sale of nearly two billion dollars in stock in the telecoms firm that he founded.

The junta has moved swiftly to investigate alleged corruption under Thaksin, who is staying in exile in London. The junta says he has no immediate plans to return home.

Sonthi said Sunday that four top aides to Thaksin, who were detained shortly after the coup, had been released. They were freed one day after Sonthi strengthened the powers of his new anti-corruption panel.