Human rights activists accused Vietnam of infringing freedom of religion after a court handed jail sentences this week to five ethnically Khmer Buddhist monks and four religious activists.

A court in the southern province of Long An condemned the men to prison terms between two and six years after finding them guilty of "abusing democratic freedoms to infringe upon state interests" and illegally detaining people, according to a police statement.

Among them, Khmer Krom Buddhist monk Thach Chanh Da Ra was given the longest, six-year prison term during a trial on Tuesday, Vietnam's Ministry of Public Security said in a statement.