Overseas bar associations and lawyers groups have issued an open letter to Chinese President Xi Jinping criticizing China's detention of lawyers and activists exactly one year after the crackdown was launched.

The letter, dated Saturday, calls on Xi to release all lawyers and others it said were unlawfully detained, and ensure that the detainees can pick the lawyers who represent them and are provided medical treatment and visitation rights.

Nearly two dozen lawyers and activists remain in detention and face charges including inciting subversion of state power.

The letter was signed by more than a dozen groups including the Hong Kong-based China Human Rights Lawyers Concern Group, the Amsterdam Bar Association, the Australian branch of the International Association of People's Lawyers and the International Commission of Jurists.