Myanmar's opposition leader is spending her 64th birthday in Yangon's Insein prison as supporters across the world continue to call for her release.

Aung San Suu Kyi is on trial for violating her house arrest after an American man swam to her lakeside residence.

A court decision is expected on Friday on her appeal to allow two previously barred witnesses to testify in her trial.

Confined for nearly 14 of the past 20 years, the Nobel laureate's birthday on Friday is being marked around the world by campaigners seeking an end to decades of military rule in Myanmar.

But the day has taken on added significance this year amid international outrage over her trial, which is widely expected to end with a guilty verdict.

In Yangon, members of her National League for Democracy (NLD) will gather at the party's dilapidated headquarters to release doves and call for the release of more than 2,000 political prisoners and a meaningful transition to democracy.

Protests are also planned outside Myanmar's embassies in major capitals around the world.

An online campaign, www.64forsuu.org, drew thousands of messages of support, including good wishes from world leaders and celebrities.

'Inspiring figure'

Aung San Suu Kyi is accused of breaking the terms of her house arrest by allowing an American intruder, John Yettaw, to stay for two days after he swam to her Yangon home in early May.

She says the trial, set to resume on June 26, is politically motivated to exclude her from next year's elections promised by the military government as a step towards democracy but derided by critics as a sham to entrench military rule.

In London, Ivan Lewis, the British foreign office minister, said Aung San Suu Kyi was being tried on "ridiculous and bogus trumped-up charges".

He said the European Union would consider further sanctions against Myanmar after the end of her trial.

Myanmar's high court agreed this week to hear arguments from Aung San Suu Kyi's lawyers to reinstate two banned defence witnesses.

But even if the ban is overturned, it is not likely to have any impact.

Mark Canning, Britain's ambassador to Myanmar, told Reuters that there was no doubt she would be found guilty and that she would probably be sentenced to a further period of house arrest, rather than prison.