A Chinese court on Friday postponed the trial of a human rights activist, Yang Maodong, after his lawyers boycotted the session to protest a denial of their right to copy court files.

Lawyer Lin Qilei quoted family members of fellow defendant Sun Desheng as saying both Yang and Sun told the court that they would remain silent without their lawyers, and the court then decided to reschedule the trial.

"The court had no choice but to announce the postponement," Lin said.

Yang, better known by his penname Guo Feixiong, is a veteran activist who advocates greater political freedom and more civic engagement in China.

He was detained in August 2013 after he organized public rallies calling for press freedom outside a media company that complained of government censorship. Authorities have charged him with gathering crowds to disrupt public order.

On Thursday, his lawyers Chen Guangwu and Zhang Xuezhong said they would not attend the court proceedings because they could not mount an effective defense after authorities did not let them copy court files crucial to the case, including videos and photos related to Yang's alleged offenses.

The court did not provide a reason for the refusal, Chen said.

Through a statement released by his lawyers late Thursday, Yang said the court had unlawfully deprived him and his legal team of a proper defense. He vowed to remain silent if the trial went ahead.

Calls to the court after the postponement rang unanswered.

New York-based Human Rights Watch urged Chinese authorities on Friday to release both Yang and Sun.

"Much of Guo's and Sun's work echoed authorities' stated policy goals, such as fighting corruption, so where's the evidence they violated any Chinese law?" Sophie Richardson, the group's China director, said in a statement.

In January 2013, Yang helped organize demonstrations and gave a speech in support of the editorial staff at the newspaper Southern Weekly in Guangzhou after the journalists said a New Year's message that called for rule by the constitution was altered because of censorship.

Authorities have accused Yang of disturbing public order, but his supporters say the rallies were orderly.

Yang's lawyers said he denies any guilt.