The appeal trial of a high-profile group of Vietnamese dissidents jailed for trying to overthrow the communist regime is scheduled for May 11, a court source said Wednesday.

Their case, originally tried in January, was the most prominent in a series of arrests and convictions of dissidents and bloggers over the past year. It led to criticism from the United States, European Union and Britain.

Human rights lawyer Le Cong Dinh, Internet entrepreneur Tran Huynh Duy Thuc, and Le Thang Long, have asked the higher court to review their case, said the appeal court source in southern Ho Chi Minh City.

At their initial trial, Thuc received a 16-year sentence while Dinh and Long got five years each after the court convicted them of a well-organised non-violent campaign, in collusion with "overseas exile reactionary organisations", aimed at overthrowing the government with the help of the Internet.

A fourth dissident, French-trained computer expert and blogger Nguyen Tien Trung, was jailed for seven years at the same trial.

The court source said Trung did not appeal.

He will, however, be present at the hearing, said Doan Thai Duyen Hai, his lawyer.

Analysts, rights groups and diplomats have described a worsening human rights situation in Vietnam, where at least 20 activists have been jailed since October.

(Source: AFA)