YANGON: Myanmar's pro-democracy leader Aung San Suu Kyi went on trial on Monday at the country's notorious prison as activists vowed to stage protests across the Southeast Asian nation until she is freed.

She faces up to five years' imprisonment on charges that she violated conditions of her yearslong detention by sheltering an American man who swam to her lakeside home earlier this month.

More than 100 Suu Kyi supporters were able to get through the outer circle of barricades around Insein prison in Yangon, but not the inner one that was closely guarded by armed police and pro-regime supporters. One young protester was seen being taken away by police.

A spokesman for Suu Kyi's defence team said the court rejected their request to open the trial to the public and media. He said today's session was largely procedural and included a police officer appearing as a prosecution witness. He said the trial would resume on Tuesday.

Suu Kyi had been scheduled to be freed on May 27 after six consecutive years of house arrest, but the ruling junta was widely expected to yet again extend her detention period.

International lawyers say this would have been illegal under Myanmar's own laws.

The latest charges are widely seen as a pretext for the government to keep Suu Kyi detained past elections it has scheduled for next year as the culmination of a "roadmap to democracy" which has been criticised as a fig leaf for continued military control.

The ambassadors of Britain, France, Germany and Italy as well as an Australian diplomat were barred from entering the prison, but the US consul was allowed into the prison compound since a US citizen, John William Yettaw, also was on trial along with Suu Kyi.

Yettaw's motives for entering Suu Kyi's compound earlier this month remain unclear and her supporters have expressed anger at him for getting the Nobel Peace laureate into trouble. Suu Kyi's lawyers have said he was not invited to her residence, and that she told him to leave.

US Embassy spokesman Drake Wiesert said it was unclear if the consul would be allowed to attend the court proceedings, or whether Yettaw was represented by a lawyer.

Security forces blocked all roads leading to the prison and police were stationed at key intersections in the city.

Several hundred riot police, many armed with guns, batons and shields, guarded the perimeter of Insein, where the regime has for years incarcerated political prisoners.