Vietnamese police have detained a well-known human rights activist for spreading propaganda against the communist state as the ruling Communist Party prepares for its five-year congress early next year.

Nguyen Van Dai, 46, was taken into police custody and his house in the capital Hanoi was searched on Wednesday, the Ministry of Public Security said in a brief statement. The case was being investigated in accordance with the law, it said.

Dai, former human rights lawyer, was arrested in 2007 and sentenced to five years in prison on charges of spreading anti-state propaganda. An appeals court later reduced the jail term to four years.

The Vietnam Communist Party is preparing for its congress set for early next year.