YANGON: US Senator Jim Webb arrived in Myanmar Friday for historic talks with military supremo Than Shwe, the first ever meeting between a senior American official and the junta chief, officials said.

The visit comes despite the regime's decision this week to extend the house arrest of pro-democracy leader Aung San Suu Kyi, prompting international outrage and an expression of "serious concern" by the UN Security Council.

Webb, a Democrat who is close to President Barack Obama, touched down in the ruling generals' bunker-like capital Naypyidaw after flying in from Laos, Myanmar officials said.

"The Senior General will meet Jim Webb tomorrow," one Myanmar official said on condition of anonymity, adding that Webb is scheduled to travel to the commercial hub Yangon later Saturday, the official said.

The US embassy in Yangon confirmed that Webb was due to arrive but said it had not received confirmation from the capital. His office also said on Thursday that he was due to meet Than Shwe.

The reclusive Than Shwe ordered Suu Kyi to serve another 18 months of house arrest on Tuesday after a court convicted her and an eccentric American man, John Yettaw, who swam to her lakeside home.

The move puts the 64-year-old Nobel peace laureate out of the picture for elections promised by the junta in 2010. Critics say the polls are a sham aimed at legitimising the regime's grip on power.

Diplomats have played down suggestions that Webb -- a hard-nosed Vietnam veteran who chairs the Senate Foreign Relations subcommittee on East Asia and Pacific affairs -- could win an amnesty for Yettaw during his visit.

Yettaw was sentenced to seven years of hard labour and imprisonment.

But a Western diplomat in Yangon said the "significant" visit by Webb would likely focus on the terms of a possible deal to win some form of early release for the 54-year-old Missouri man.

Webb's visit could also herald a change in the tough US stance towards Myanmar after the Obama administration said earlier this year that it would review its policy on Myanmar.

Secretary of State Hillary Clinton last month held out the carrot of possible investment if the junta frees Suu Kyi, although she warned that there were concerns over nuclear cooperation between North Korea and Myanmar.

In April, Webb himself said that the United States should take a new approach of "constructive" engagement with Myanmar with an aim of lifting sanctions.

But he said in July that the trial of Suu Kyi would make this task more difficult.

Suu Kyi's National League for Democracy (NLD) said four senior members of the party had been invited to Naypyidaw on Friday "to meet with an important person," although it was not clear if it was Webb, Than Shwe or both.

Spokesman Nyan Win welcomed the UN Security Council statement Thursday and hailed the European Union's decision the same day to extend sanctions against the junta, including the judges in the trial.

"These moves show that the whole world wants justice for Daw Suu. We have the same attitude," said Nyan Win.

The White House Thursday welcomed Webb's visit, which is also the first by a member of Congress in more than a decade, saying he would convey "strong" US views of good governance to the junta's leaders.

Myanmar's state media said Friday that a decision by Than Shwe to commute the court's original sentence of three years' hard labour for Suu Kyi showed that the government was ready to respond too.

"By issuing the directive, the (Myanmar) government has paced a giant step towards change," it said.

Suu Kyi has been in detention for 14 of the last 20 years since the junta refused to recognise the NLD's victory in elections in 1990.

In Bangkok, Thailand said it was "seeking a consensus" with the Association of Southeast Asian Nations (ASEAN) to ask Than Shwe to officially pardon Suu Kyi.

Communist Laos however on Friday followed neighbouring Vietnam in saying that the trial took place in accordance with the country's law, and underlined its stance on not interfering in ASEAN nations' internal affairs.