The trial in the central province of Phu Yen is set to last five days.

The leader and 21 other members of the group - called Hoi Dong Cong Luat Cong An Bia Son in Vietnamese - were all in the dock, the clerk told AFP, requesting anonymity.

Rights groups say charges of spreading anti-state propaganda and attempting to overthrow the regime are routinely laid against peaceful dissidents in a country where the ruling Communist Party forbids political debate.

The accused group's name translates as Council for the Laws and Public Affairs of Bia Son, but there is scant information about its aims beyond Vietnamese police accounts, which depict it as a terrorist group.

Bia Son is a mountain in Phu Yen province.

The 22 are charged with carrying out "activities aimed at overthrowing people's administration". In theory this carries the death penalty but the communist regime has never executed anyone for political crimes.

The group was run "non-violently" by its 65-year-old leader Phan Van Thu between 2003 and his arrest in February last year, according to state media. But it is little known in Vietnam.

The Vietnam News Agency said the group has around 300 members in several central and southern cities and provinces.

The group sought to "wear down people's trust in the party and state leadership and create suspicion and concern about the current regime", it reported, adding that the group received funding from overseas Vietnamese.

Dozens of political activists have been jailed since Vietnam, a one-party state, began a new crackdown on free expression in late 2009. Earlier in January courts jailed 14 dissidents, including Catholics, bloggers, students and a farmer, in two different trials, for the same charge of attempting to overthrow the government.

Agence France Presse - January 28, 2013