YANGON - Myanmar again barred diplomats and journalists from the trial of Aung San Suu Kyi Thursday, as international pressure mounted on the military junta to drop the case against the pro-democracy icon.

The regime had unexpectedly opened up the hearing at the notorious Insein prison for just one day on Wednesday, in an apparent concession to global criticism of its treatment of the Nobel Peace Prize winner.

But it clamped down again Thursday, despite a warning from US Secretary of State Hillary Clinton over the "outrageous" charges against the 63-year-old and a pledge by UN chief Ban Ki-moon to visit the country.

"Only for one day were diplomats and press allowed," a Myanmar official told AFP on condition of anonymity.

About 30 members of her National League for Democracy (NLD) party, including the country's former longest-serving political prisoner, Win Tin, kept up a vigil outside the prison as the trial resumed Thursday, witnesses said.

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

A smiling, healthy-looking Aung San Suu Kyi 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 proceedings on Wednesday along with 10 journalists from local and foreign organisations.

Aung San Suu Kyi later met envoys from Thailand, Singapore and Russia, expressing hope that "it was not too late for something good to come out of this unfortunate incident", a Singapore government statement said.

State television showed footage of her talking animatedly to the diplomats and 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.

Yettaw, 53, and two political aides who live with Aung San Suu Kyi are also on trial.

The US national spent two nights at the residence in what his family have described as a well-intentioned stunt to offer support to her.

The regime has kept Aung San Suu Kyi in detention 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.

Critics say the junta wants to keep her locked up ahead of elections planned for next year under a controversial "roadmap to democracy" that enshrines a role for the military in government.

In Washington, Clinton said the regime's treatment of Aung San Suu Kyi would automatically make the polls "illegitimate because of the way that they have treated her".

She added that it was "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".

UN chief Ban said he was "deeply concerned" about the situation in Myanmar and said he would bring up the issue with junta leader Senior General Than Shwe.

"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," he told CNN.

Leading international jurists called for the UN Security Council to follow the precedent of Rwanda and the former Yugoslavia and hold an inquiry in Myanmar, saying the regime could be guilty of crimes against humanity.

"With Burma, there has been no such action from the UN Security Council," said the report published by Harvard Law School.