A Chinese court has sentenced prominent dissident Chen Xi to 10 years in prison for inciting subversion.

After a short trial Monday in Guiyan – the provincial capital of Guizhou province – Chen maintained his innocence, but said he would not appeal the guilty verdict. Chen is a veteran of the 1989 Tiananmen democracy protest movement.

Activists believe the charge was related to essays the 57-year-old wrote on advancing political reform and improving human rights in China.

On Friday, veteran democracy activist Chen Wei was sentenced in the southwestern province of Sichuan to nine years behind bars for subversion.

U.N. High Commissioner for Human Rights Navi Pillay responded in a news release Monday, saying she was deeply concerned about the verdict and extremely harsh sentence in Chen Wei's trial.

Pillay also criticized a decision a week earlier to send human rights lawyer Gao Zhisheng back to prison for three years, after a Beijing court ruled he had violated the terms of his probation.

She called on Chinese authorities to release any person detained for peacefully exercising the right to freedom of expression.

Inciting subversion is a charge often used to punish dissidents critical of the ruling Communist Party.