Chinese authorities are increasingly resorting to attacks and secret detentions in a crackdown on activist lawyers that has worsened this year amid government efforts to prevent the growth of an Arab spring-style protest movement, Amnesty International said.

Amnesty said the government has also suspended or revoked lawyers' licences to stop them from taking sensitive cases, such as defending pro-democracy dissidents, members of banned religious movements or government critics.

"Intimidation, harassment, violence, arbitrary detention were all increasingly used against lawyers and their families in 2010," the group said, in a report released on Thursday detailing the crackdown over the past two years. "Such acts are carried out in more and more blatant ways, with officials abandoning even the pretence of obeying the law."

China has kept a steady drumbeat of pressure on the small community of human rights lawyers who already face numerous difficulties working in China's tightly controlled legal system to press for civil liberties and combat abuse of power.

The pressure intensified in February as the government launched one of its broadest campaigns of repression in years. Dozens of activists, lawyers and bloggers have been questioned, detained or simply have disappeared in an effort to quash even the possibility of a pro-democracy movement forming along the lines of those sweeping the Arab world.

Among them are prominent rights lawyer Teng Biao, a law professor at the China University of Political Science and Law in Beijing, who disappeared in mid-February and resurfaced more than two months later. Beijing attorney Jiang Tianyong, who worked on cases involving Aids activists and freedom of religion, also vanished for two months.

Many of the lawyers are refusing to speak to journalists, suggesting possible intimidation by authorities.

Authorities also use administrative measures to pressure lawyers. Amnesty International estimates that 30 to 40 rights lawyers have lost their licences either temporarily or permanently since 2008, the London-based group's Asia Pacific deputy director, Catherine Baber, said.

One of the most high-profile targets of the crackdown on rights lawyers over the past few years is Gao Zhisheng, a charismatic and pugnacious lawyer who represented religious dissenters and advocated constitutional reform.

Gao, who has been missing for more than a year, has drawn international attention for the unusual length of his disappearance and for his earlier reports of torture he said he endured in detention.

The ministry of public security and Beijing's municipal public security bureau did not respond to a request for comment on the report.