BEIJING (Reuters) - Chinese authorities have formally charged a prominent rights activist with subversion of state power after holding him incommunicado for six months, his wife said on Tuesday.

Jiang Tianyong defended high-profile dissidents and practitioners of Falun Gong, the banned spiritual movement, before being disbarred in 2009. He continued to speak out against government crackdowns on rights lawyers.

Jiang disappeared in November 2016 after traveling to central China’s Changsha city to provide advice and support to a fellow rights lawyer, Xie Yang. In December, authorities confirmed they were holding Jiang on suspicion of inciting subversion.

On Monday, six months later, the longest a suspect can be held without charge under Chinese law, his father received an official charge notice in the post, according to Jiang’s wife, Jin Bianling, who now lives in the United States.

The notice, dated May 31, said Jiang was being held on suspicion of subverting state power, a more serious crime, and was being held in Changsha City Number One Detention Centre, according to photos of the document seen by Reuters.

The notice is the first official confirmation of Jiang’s whereabouts that she or his parents have had in six months, Jin told Reuters by phone.

Jin said she was worried about Jiang’s treatment in custody and believes authorities may be attempting to force him to confess.

No one answered the publicly listed phone number for the Changsha detention center.

In May, Jin said that Jiang may have been tortured until he was unable to stand. The authorities released a video of Jiang walking in shorts to refute the claim, which she said was unconvincing.

China has vowed to deal with problems of torture, beatings and forced confessions in its criminal justice system.

“The crimes he (Jiang) is suspected of keep changing,” Jin said. “It seems Jiang Tianyong has not admitted to any crimes, so they are going to keep torturing him until he confesses.”

Although Jiang’s family and lawyers have been unable to speak to him, state media released a number of interviews with Jiang in March, where he appeared to confess to having helped fabricate accounts of Xie Yang being tortured.

Xie later denied he was harmed during a public trial in early May, where he admitted to charges of subverting state power.

Jin says that the state media accounts of what Jiang said were either themselves fabricated or evidence of Jiang being pressured by the authorities into giving false testimony.