The men, aged between 27 and 38, were given sentences of between three and seven years at a one-day trial Wednesday at a court in the northwestern province of Lai Chau, the Communist Party mouthpiece Nhan Dan said.

One of the men, Trang A Cho, had been sought by police since July 2011 for carrying out "propaganda against the State" and seeking to establish a "Hmong Kingdom" to "replace the State of Vietnam," the report said.

The four join eight other Hmong men already jailed for "disturbing security" at a mysterious religious gathering last year, which Vietnamese authorities describe as an attempted separatist uprising.

In May 2011 thousands of Hmong convened in the remote northwest apparently awaiting the arrival of a "messiah". The gathering was broken up by authorities, in circumstances which remain unclear.

At the time unconfirmed reports said dozens of Hmong were killed or wounded by troops but Vietnamese officials have not said whether there was any military involvement.

Officials 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, 2011, was key to the timing of the gathering.

A local government leader later claimed that the Hmong were armed.

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 - December 13, 2012