A prominent Vietnamese activist lawyer is expected to go on trial Wednesday amid tight security, as campaigners threaten street demonstrations and international rights groups demand his immediate release.

Le Quoc Quan is due to appear at the Hanoi People's Court early Wednesday on charges of tax evasion, the Hanoi external relations department said in a letter sent to AFP and other foreign news agencies.

Vietnamese authorities frequently cancel such trials at very short notice, particularly if there is a risk of public protest.

The trial was originally scheduled for July 9 but postponed at the last minute.

The letter warned foreign news agencies not to bring "recording or communication equipment" to the court.

Activists told AFP that they were being kept under virtual house arrest by police in a bid to prevent them attending the trial of the Catholic lawyer, who blogged on a range of sensitive topics prior to his arrest including civil rights, political pluralism and religious freedom.

Le Quoc Quyet, Quan's brother, said many activists were gathering at a Hanoi church and planning to march towards the court early Wednesday to protest the 41-year-old's case.

"I am not sure if we will be allowed to go ahead, but we will try," he said, adding that he was also not certain if police would allow him to attend his brother's trial.

Le Quoc Quan has been in detention since December 2012.

He has been accused of attempting to avoid corporate income tax of more than $20,000 at a company he founded in 2001, according to the state-run VietnamNet online newspaper.

Another prominent Vietnamese blogger, best known by his pen name Dieu Cay, was charged with tax evasion in 2008.

Dieu Cay, whose real name is Nguyen Van Hai, was given 30 months in jail.

He was not released after completing the sentence and was later charged with conducting anti-state propaganda and sentenced to 12 years.

New York-based Human Rights Watch has described the charges against Le Quoc Quan as "politically motivated" and called for his immediate release.

???The Vietnamese government appears to be so nervous about its position in society that it is reflexively finding ways to silence and imprison dissident after dissident,??? said Brad Adams, HRW's Asia director.

Vietnam is regularly denounced by rights groups and Western governments for its intolerance of political dissent and systematic violations of freedom of religion.

Scores of dissidents have been jailed in recent years for anti-state activity in the authoritarian country -- where the Communist Party forbids all political debate -- including 46 activists so far in 2013.

US officials said in June that Vietnam was holding more than 120 political prisoners.

Reporters Without Borders said in July that Vietnam was second only to China in the number of bloggers it detained.

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