YANGON: Myanmar's military junta put the trial of opposition leader Aung San Suu Kyi back behind closed doors Thursday, after allowing diplomats and journalists to attend the hearing for just one day.

The regime had opened up the proceedings at the notorious Insein Prison near Yangon on Wednesday in an apparent concession to fierce international criticism of the charges against the Nobel Peace Prize winner.

"The press will not be allowed today (Thursday). Only for one day were diplomats and press allowed," a Myanmar official told AFP on condition of anonymity.

The Myanmar state clamped down again on Thursday, despite a warning from US Secretary of State Hillary Clinton that elections scheduled in 2010 would automatically be "illegitimate" because of the democracy icon's treatment.

The UN chief Ban Ki-moon has also expressed his doubts over the trial saying he was "deeply concerned" by the legal case against Aung San Suu Kyi and would visit Myanmar as soon as possible to urge the junta's chief to release her.

"I'm going to visit Myanmar as soon as possible. Now I am very serious in discussing with (the) government of Myanmar when I could be able to visit Myanmar," Ban told CNN in an interview filmed on Wednesday.

Earlier diplomats had said that they had been informed they would only be allowed into the trial for one day, but the situation for the media had been unclear until official confirmation that they would be barred came on Thursday.

A smiling, healthy-looking Aung San Suu Kyi, 63, had thanked diplomats for coming to the trial on Wednesday and said she hoped to meet them again in "better days."

Authorities allowed one diplomat from each of the 30 foreign embassies in Yangon to attend the courtroom, while Aung San Suu Kyi later held a separate meeting with envoys from Thailand, Singapore and Russia.

Aung San Suu Kyi State television showed footage of her striding briskly from a car to the meeting and then talking animatedly to the diplomats inside a "guest house," which an announcer said was in fact the prison's officer's mess.

It is the first moving footage of her for several months.

It said Aung San Suu Kyi had told the envoys she was in "good health and convenient accommodation has been provided." Medical specialists had visited her Wednesday and she was receiving daily health care at the prison, it added.

Five journalists working for foreign news organisations and five from local groups were also allowed into the trial, which had previously only been reported on by the tightly controlled state media.

Aung San Suu Kyi faces up to five years in jail if convicted of charges of breaching her house arrest stemming from an incident earlier this month in which an American man, John Yettaw, swam to her lakeside house.

Yettaw, 53, spent two nights at the residence house in what his family have described as a well-intentioned stunt to offer support to her. He also faces trial, along with two political aides who live with Aung San Suu Kyi.

The regime has kept her in jail or under house arrest for 13 of the past 19 years. It filed the charges against her just weeks before a May 27 deadline when her latest six-year spell of detention expires.

In Washington, Clinton told a Senate subcommittee that the Barack Obama administration was pushing for her release.

"But it is outrageous that they are trying her and that they continue to hold her because of her political popularity and they intend to hold elections in 2010," the chief US diplomat said.

These elections from the beginning "will be illegitimate because of the way that they have treated her," she continued.

"So it is our hope that this baseless trial will end with a quick release of her and then a return to some political involvement eventually by her and her party," she added.

Critics say the elections are a sham designed to entrench the junta's power, as they are being held under a controversial constitution forced through in 2008 which gives the military a role in any government.

The regime refused to recognise a landslide victory by Aung San Suu Kyi's party in the last elections to be held in Myanmar in 1990. The military has ruled Myanmar since 1962.