She Wanbao, who helped set up the outlawed Chinese Democracy Party (CDP), was charged with attempting to subvert state political power.

The BBC's Rupert Wingfield-Hayes: "The most intense suppression in recent yeras"

Fellow activist Liu Xianbin is due to stand trial on Friday on the same charges.

Two other CDP members, Gong Hongming and Zha Jianguo, were given sentences of eight and nine years on Monday.

Reports say the communist authorities have stepped up their campaign against the opposition in the run up to the regime's 50th anniversary on 1 October.

Tiananmen crackdown

At least eight CDP activists have reportedly been jailed since Nato's bombing of China's embassy in Yugoslavia in May, which put a freeze on China-US ties including dialogue on human rights.

CDP leader Xu Wenli is serving 13 years

The Hong Kong rights group, the Information Centre of Human Rights and Democratic Movement in China, says 20 members of the party could be tried this month.

It said Mr She was also ordered to be stripped of his political rights for three years after his release following a three hour trial in the Sichuan city of Guangyuan.

Reports say Mr She had previously spent four years in prison for taking part in the 1989 democracy movement which lead to the military crackdown in Tiananmen Square in Beijing.

Fourth trial

Fellow activist Mr Liu, who was also involved in the 1989 student protests, helped establish the CDP in Sichuan.

He spent two years in jail following the crackdown on the democracy movement.

The CDP was set up in 1998 during an apparent political thaw in China.

But Beijing moved to crush the group at the end of last year, sending scores of members to jail or to labour camp.