Myanmar democracy icon Aung San Suu Kyi marked her 65th birthday under house arrest yesterday as activists held protests around the globe and world leaders called for the junta to free her.

The military regime has kept the Nobel laureate in detention for almost 15 years and she has been barred from running in upcoming elections that critics have denounced as a sham aimed at entrenching the generals' power.

Suu Kyi's party won the last polls in 1990 but was never allowed to take office. A UN working group last week pronounced her detention a breach of international human rights law, prompting new calls for her release.

In a birthday message, US President Barack Obama hailed Suu Kyi's "determination, courage and personal sacrifice in working for human rights and democratic change".

"I once again call on the Burmese government to release Aung San Suu Kyi and all political prisoners immediately and unconditionally and to allow them to build a more stable, prosperous Burma that respects the rights of all its citizens," he said, using the country's former name.

The woman known in Myanmar simply as 'The Lady' remains the most powerful symbol of freedom in a country where the army rules with an iron fist.

The opposition leader spent the day at her lakeside mansion in Yangon, where she lives with two female assistants, cut off from the outside world without telephone or internet access.

About 400 of her supporters held a party at one of their houses in northern Yangon in her absence. Plain-clothes police outside photographed and filmed people attending the event.

"We, the NLD members, Daw Suu's friends and colleagues, pray for her release soon," said Win Tin, a former political prisoner and senior National League for Democracy (NLD) figure. 'Daw' is a term of respect in Myanmar.

Suu Kyi's supporters, some of whom wore T-shirts bearing her image, freed caged birds, prayed in front of her portrait and cut a birthday cake.

"The most important thing is the release of Daw Aung San Suu Kyi," said her lawyer Nyan Win. "Although she is in detention, Daw Aung San Suu Kyi's spirit has not been diminished at all."

NLD members are planting about 20,000 trees around Myanmar to mark her birthday and sent spicy food to her home to share with workers doing renovations.