Myanmar opposition icon Aung San Suu Kyi said she hoped for "better days" Wednesday as the ruling junta unexpectedly allowed diplomats and reporters to attend her internationally condemned trial.

The 63-year-old smiled and looked healthy as she thanked foreign envoys for coming to Insein Prison in her first public comments since she was charged last week with breaching her house arrest, an AFP reporter inside the court said.

"Thank you very much for coming and for your support," Aung San Suu Kyi, wearing pink Burmese traditional dress, said inside the courtroom at the end of the third day of the trial.

"I can't meet you one by one, but I hope to meet you all in better days," she added.

Aung San Suu Kyi then went for a meeting with the ambassadors of Singapore and Russia and a senior diplomat from Thailand at the so-called "guest house" inside the prison compound where she is being held.

The Nobel Peace Prize winner 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.

The surprise move by the military regime to allow some diplomats and media access to the trial followed intense international pressure and a scathing condemnation by Myanmar's normally placid Southeast Asian neighbours.

Authorities held the first two days of hearings behind closed doors and had turned away European diplomats on Monday, but on Wednesday said representatives from all 30 foreign embassies would be allowed in.

The regime also allowed five journalists from foreign news organisations and the same number from local organisations to report on the hearing.

Details had previously emerged only in state media or through Aung San Suu Kyi's lawyers.

But diplomats said they did not have much confidence in the trial.

"I think this is a story where the conclusion is already scripted," the British ambassador to Yangon, Mark Canning, told the BBC.

"I don't have any confidence in the outcome. While the access we had today was very welcome, it doesn't change the fundamental problem."

Aung San Suu Kyi has spent 13 of the last 19 years in detention since the regime refused to recognise her party's landslide victory in the last elections to be held in Myanmar in 1990.

Thailand was picked because it holds the chairmanship of the Association of Southeast Asian Nations (ASEAN), while the Singaporean envoy is the doyen of Yangon's diplomatic corps and Russia heads the UN Security Council.

Asked to explain the regime's apparent change of heart, a western diplomat said that following international pressure on the ruling generals, particularly by ASEAN, "one has to ask if all these pressures played a role."

EU nations have said they are mulling tighter sanctions over the handling of the trial, while US President Barack Obama formally extended American sanctions last week.

Critics say the junta has trumped up the charges to keep Aung San Suu Kyi locked up during elections due next year, and also to beat a 27 May deadline when her latest six-year period of detention expires.

The trial on Wednesday heard from only one police witness about the arrest of Yettaw, who used a pair of homemade flippers to swim across the lake before spending two days at Aung San Suu Kyi's residence.

Yettaw, a 53-year-old former US army veteran from Missouri, and two female aides who live with the opposition leader are also on trial.

Aung San Suu Kyi's lawyers have described Yettaw as a "fool" and said she only allowed the American, reportedly a diabetic, to stay after he complained of suffering from leg cramps.