A prominent Chinese human rights lawyer says he was blocked from leaving the country to participate in a U.S. State Department-sponsored studies program.

Chen Jiangang said he was pulled aside Monday at Beijing airport and told by a customs agent that he was forbidden to leave because he had represented another lawyer, Xie Yang, in an earlier case.

He said he was told that the U.S. government's acceptance of him as a visiting scholar also made him suspect.

As Xie's former lawyer, Chen had helped release his client's account of torture, for which he was himself detained.

Xie was released in mid-2017 after allegedly confessing in court to collaborating with foreign organizations and media to smear and subvert Communist Party rule.

Government critics frequently face such exit bans as punishment.