The U.N. human rights chief says he has raised concerns with Chinese authorities over a crackdown against lawyers, advocacy groups and government critics in recent months.

Zeid Raad al-Hussein says there is a "worrying pattern" in China for civil society and notes that states have a duty to protect lawyers, journalists and members of non-governmental organizations.

The office of the High Commissioner for Human Rights said in a statement Tuesday that police have detained about 250 human rights lawyers, legal assistants and activists since a "nationwide crackdown" began in July, though many have since been released.

Zeid also expressed concern about recent disappearances of booksellers from Hong Kong, and noted that leading human rights lawyers Li Heping and Wang Yu are among those facing a "subversion of state power" charge.