BANGKOK, August 6, 2008 (AFP) - US President George W. Bush vowed to 'seek an end to tyranny' in Myanmar and called on the regime to free democracy leader Aung San Suu Kyi, according to a copy of a speech he will deliver Thursday.

'We seek an end to tyranny in Burma,' he was to say, referring to the country by its previous name.

'America reiterates our call on Burma's military junta to release Aung San Suu Kyi and all other political prisoners. And we will continue working until the people of Burma have the freedom they deserve.'

The advance copy of the speech on US policy toward Asia was released as Bush headed to Bangkok from Seoul, on a regional tour ahead of his visit to Beijing for the opening of the Olympic Games on Friday.

The US president was set Thursday to meet in the Thai capital with exiled political dissidents from Myanmar, on the eve of the 20-year anniversary of a pro-democracy uprising there which was crushed by the army, leaving 3,000 dead.

His wife Laura planned to visit a clinic and Myanmar refugees on the border, where more than 120,000 civilians who have fled brutal junta crackdowns on ethnic rebel armies live in cramped camps.

Laura Bush has been an outspoken critic of the Myanmar junta, and the president's speech hailed her efforts along with the work of others trying to bring change to a country ruled by the military since 1962.

'This noble cause has many devoted champions, and I happen to be married to one of them,' he said in the prepared remarks.

Aung San Suu Kyi led her National League for Democracy (NLD) party to election victory in 1990, but instead of recognising the result the junta kept her under house arrest, where she has now spent most of the last 19 years.

The generals have suppressed any sign of dissent, and more than 2,000 political prisoners are believed to be behind bars in the isolated nation.

On Friday, activists in Myanmar will silently mark two decades since the August 8, 1988 uprising, when students led activists, Buddhist monks, and even young military cadets into the streets, only to face a massacre by the army.

Last year, protesters again poured onto the streets to rally against economic hardship and junta rule. This time, 31 people were killed in the resulting crackdown, the United Nations has said.

The United States has been the most vocal critic of the junta, and has a patchwork of economic sanctions against the regime. These sanctions were strengthened after the crackdown last September.