In May 2011, thousands of Hmong, a mostly Christian ethnic group, gathered in Vietnam's remote northwest apparently awaiting the arrival of a "messiah".

The gathering was subsequently dispersed by authorities, in circumstances which remain unclear.

The eight defendants, who appeared in court Tuesday in the northwestern province of Dien Bien, were charged with "disturbing security", the communist party newspaper Nhan Dan reported.

Two of them received two-and-a-half year jail terms while the other six were given two-year sentences. They will all also have to spend two years under house arrest following their release, the report said.

"This is a serious sentence, but it also expresses the humanitarian (side of) Vietnamese law," as the jail terms could have been much longer, the Tin Tuc newspaper reported.

Officials had said the Hmong were lured by unidentified "individuals with ill intentions" who spread rumours that a "king" would arrive and lead them to a promised land.

According to Britain-based religious freedom group Christian Solidarity Worldwide (CSW), the Hmong have "a mythical belief in their culture that a 'messiah' figure will appear and found a Hmong kingdom".

CSW said the prophecy of US radio preacher Harold Camping, who claimed the world would end on May 21 last year, was key to the protest's timing.

There were unconfirmed reports at the time that dozens of Hmong were killed or wounded by troops when the protest was broken up but Vietnamese officials have not said whether there was any military involvement.

A local government leader later claimed in an interview with an army newspaper that the protestors had been armed.

"The Vietnam authorities have continuously prevented independent monitors from assessing what actually happened" and had "presented a one-sided view of events", said Phil Robertson, Asia deputy director for Human Rights Watch.

"The recent announcement of prison sentences for protest organisers for allegedly disturbing social order raises many questions, such as what did the persons actually do to be prosecuted and receive these sentences."

The incident was the country's worst case of ethnic tension since about 2,000 Montagnards fled to Cambodia over 2001 and 2004 after troops crushed protests in the central highlands.

Some of the Hmong helped US forces against North Vietnam during the secret wartime campaign in neighbouring Laos, and faced retribution after the communist takeover.

Agence France Presse - March 15, 2012