YANGON (AFP) - Myanmar faced intense international pressure Friday to free pro-democracy icon Aung San Suu Kyi after she was imprisoned ahead of a new trial next week for breaching the terms of her house arrest.

The United States led Western calls for the immediate release of the Nobel Peace laureate while rights groups urged the UN Security Council to help the 63-year-old, whose trial is due to start in jail on Monday.

The ruling military junta took Aung San Suu Kyi from her home on Thursday to Yangon's notorious Insein prison, where she was charged over a bizarre incident in which an American man swam to her lakeside residence.

There was no comment from Myanmar's secretive regime, which has kept the frail opposition leader in detention for most of the last 19 years and now looks set to do so past controversial elections that are due next year.

New York-based Human Rights Watch called on UN Secretary General Ban Ki-moon to press the authorities for her release, accusing the junta of taking advantage of the US man's "bizarre stunt" to keep Aung San Suu Kyi detained.

Amnesty International demanded that the UN Security Council "urgently intervene" to secure her release. It also urged Myanmar's powerful neighbours, China and India, to press the generals.

US Secretary of State Hillary Clinton said she was "deeply troubled" by the "baseless" case laid against Aung San Suu Kyi just days before her latest six-year detention was to have expired.

UN chief Ban said he was "gravely concerned".

Britain, France and other Western nations - which like the United States have imposed sanctions on the country formerly known as Burma - condemned the decision and said it did not bode well for the 2010 elections.

A group of eminent statesmen including South African Archbishop Desmond Tutu and former US President Jimmy Carter also demanded her release.

Indonesia became the first of Myanmar's partners in the 10-member Association of Southeast Asian Nations (ASEAN) to call for the junta to release Aung San Suu Kyi and drop the "arbitrary" new charges against her.

Thailand, which borders Myanmar, "hoped" that she would be freed and said the government should not use her trial as an excuse to extend her detention, but there was no reaction from India or China.

Myanmar authorities are currently holding Aung San Suu Kyi and her two maids, who were also charged, at a house inside the grounds of Insein Prison pending the trial, her lawyers have said.

Stopped by the junta from taking power after leading her National League for Democracy party from winning a landslide victory in the country"s last election in 1990, she now faces a maximum jail term of five years.

The case centred around a mysterious US national, John Yettaw, who was arrested last week after using a pair of homemade flippers to swim across a lake to Aung San Suu Kyi's crumbling house.

Reportedly a Mormon father of seven and Vietnam War veteran, the heavy-set 53-year-old also faces charges of violating the restricted area around her home and breaching immigration conditions.

His motives remain unclear but Irrawaddy magazine, published by Myanmar exiles in Thailand, dismissed speculation about the coincidental timing of the incident before the expiry of her detention order.

It said he was "simply a weird character who acted alone," while Aung San Suu Kyi's lawyers have described him as a "fool."

Yettaw had also met with Myanmar exile groups in Thailand and reportedly told them he was working on a faith-based book on heroism, the magazine said.

Aung Naing Oo, a Myanmar analyst based in Thailand, said that the Western outrage over the new charges against Aung San Suu Kyi would likely have little impact on junta leader Senior General Than Shwe and his deputies.

"The problem is the Burmese military don't care about international opinion," Aung Naing Oo told AFP.