Chinese police appeared to have arrested a group of dissidents in both Beijing and Guangzhou in an apparent attempt to silence the 25th anniversary of the Tiananmen Square massacre on June 4.

Pu Zhiqiang, a well-known lawyer, and two others have been formally arrested. Three others have disappeared. Six people are believed to be in custody in Guangzhou. A liberal film director, Shen Yongping, has also disappeared.

"I believe the authorities are detaining Pu now so that he can't do anything between now and the anniversary and so his detention will create a panic and terror among those who wish to remember that day," Hu Jia, a Beijing activist and one of Pu’s closest friends, said. Hu himself has been under house arrest since February, he said.

Pu was a student leader during the Tiananmen protests and is now a prominent human rights lawyer in the country. Police reportedly came to his home at 4 a.m. Monday morning to arrest him. A day later they returned and confiscated files, computers and mobile phones.

Qu Zhenhong, his niece, says he was arrested under the charge of “causing a disturbance” which can carry a 5-year prison sentence. He was recently seen attending a seminar in Beijing about the Tiananmen protests that called the incident “an injustice to open fire on unarmed citizens".

Besides Pu, three others have disappeared:  Hu Shigen, a writer; Liang Xiaoyan, an academic; and Li Xuewen, a writer.

Hao Jian, a professor, and Xu Youyu, a think tank researcher have been formally arrested, both on same charges of causing a disturbance.

Beijing police have not made an official comment on Pu’s arrest. He has not been formally indicted.