One of China’s best known dissidents, Liu Xiaobo, has been formally arrested on suspicion of inciting subversion, following his detention late last year for promoting a petition calling for an end to one-party rule.

The move brings Liu a step closer to trial, and it will be a blow to human rights groups who had hoped he would be released after China passed the politically sensitive 20th anniversary of the 1989 pro-democracy Tiananmen protests.

Xinhua said on Wednesday that prosecutors approved Liu’s arrest by the Beijing police on Tuesday. “Liu has been engaged in agitation activities, such as spreading of rumours and defaming of the Government, aimed at subversion of the state and overthrowing the socialism system in recent years,” Xinhua quoted police as saying in a statement.

If indicted and convicted, the 53-year-old dissident could be sentenced to a maximum of 15 years in prison, according to Mo Shaoping, an attorney who has been barred from representing Liu because the lawyer also signed the Charter 08 petition that the dissident helped launch.