YANGON: Myanmar authorities Monday prevented the ambassadors of four European countries from entering a prison to attend the trial of opposition leader Aung San Suu Kyi, a diplomat said.

Envoys from Britain, France, Germany and Italy were turned back from the notorious Insein prison near Yangon, where security forces set up a tight security cordon with barbed wire barricades, said the western diplomat.

"The ambassadors from the EU (European Union) went to Insein prison, but they were prevented from entering and forced to turn around," the Yangon-based diplomat told AFP on condition of anonymity.

"In a lawful state, judicial hearings are public," the diplomat said.

Witnesses said an Australian diplomat was also turned away from the prison earlier but there was no immediate confirmation from the country's officials.

Aung San Suu Kyi was charged last week with breaching the terms of her house arrest after an incident in which an American man swam across a lake to reach the residence where she was being detained by the military junta.

She faces up to five years in jail if convicted at the trial which a Myanmar official said had started on Monday. The US national, John Yettaw, is also set to go on trial on Monday and faces a similar sentence.

A spokesman for the US embassy in Yangon was not immediately able to confirm whether Yettaw was receiving consular assistance at the trial.