BEIJING | The last time prominent Chinese lawyer Jiang Tianyong was seen or heard from, he was visiting his brother in a Beijing suburb. Police grabbed him and threw him into a waiting van, pushing aside his elderly mother who had clung on to the vehicle.
Mr. Jiang is among dozens of well-known lawyers and activists across China who have vanished, been interrogated or criminally detained for subversion in recent weeks. Human rights groups say the repression is on a scale and intensity not seen in many years.
Activists say China's massive security apparatus is using the government's anxiety over possible Middle East-inspired protests as a pretext for the crackdown.
"None of them will tell me anything about why he was taken away or where he has been taken to," Mr. Jiang's wife, Jin Bianling, said this month.
She said that after her husband's disappearance in February, a Beijing police officer told her that "the case was being handled," meaning he was under investigation. Her repeated efforts to get more details from police have been fruitless.
More than 100 people have been questioned or followed by police or placed under house arrest, the Hong Kong-based Chinese Human Rights Defenders said in a recent statement. Mr. Jiang and others who have disappeared for weeks were at risk of being tortured to extract confessions, the group warned.
Nicholas Bequelin, senior Asia researcher for Human Rights Watch, said the crackdown is even more serious than the one in December, when the Nobel Peace Prize was awarded to a jailed Chinese dissident, Liu Xiaobo.
Mr. Bequelin said it is also more extensive than when police questioned and detained activists involved in signing Charter 08, a manifesto for peaceful democratic reform that Mr. Liu co-authored, in 2008.
"There is a sense that the authorities want to put an end to the kind of open defiance of the government by rights activists, people who have been fairly active on Twitter and other social networks who were allowed for a couple of years to do that," Mr. Bequelin said.
China employs a wide range of extralegal measures to silence independent voices, including house arrest, 24-hour surveillance and coerced stays in government guest houses.
Such actions are especially common around politically sensitive occasions such as the national legislature's annual session earlier this month.
Mr. Jiang is among a number of lawyers who have played a leading role in China's "weiquan," or "rights defense" movement, which has sought to use legal means to hold the authorities accountable for abuses of power and infringements on civil rights.
Some of the high-profile cases Mr. Jiang has taken include defending a Tibetan Buddhist cleric in 2009 against charges linked to ethnic riots in Tibet a year earlier.
Mr. Jiang is also an outspoken advocate for people demanding compensation after contracting HIV and AIDS from selling their blood or receiving tainted blood transfusions, an issue Beijing sees as highly sensitive.
Mr. Jiang needs medication daily for high blood pressure, but police have refused to convey his medicine to him, his wife said.
"I worry about him all the time. What if the police are torturing him? But I don't know what I can do," she said.
Also missing are Teng Biao, a law professor at the China University of Political Science and Law, and Tang Jitian, who was disbarred last year after he represented a member of the outlawed Falun Gong spiritual movement.
Ding Fangguan, an activist who writes under the pen name Gu Chuan, also is missing.
The three lawyers were taken away Feb. 19, three days after they attempted to meet with a group of other lawyers to discuss ways to help Chen Guangcheng, an activist being held under house arrest with his family despite having already served jail time.
The Chinese human rights group said 11 writers and activists in provinces ranging from southwestern Sichuan to coastal Jiangsu to northern Heilongjiang have been officially detained on suspicion of "inciting subversion of state power," or face the more serious charges of "subversion of state power" and "endangering state security."
An official detention usually leads to prosecution in court.
The use of extralegal measures has unsettled other rights lawyers who wonder how far Beijing will stray from the rule of law that the government frequently says it promotes.
"The law gives us the biggest certainty. But what I am seeing now is that it's harder and harder to protect its authority," said Li Fangping, another prominent rights lawyer. "I am definitely concerned about my safety because of the three lawyers' disappearance."
Mr. Teng's wife, Wang Ling, said this was the lengthiest time her husband has been in police custody.
Mrs. Wang said her 5-year-old daughter has asked after her father. "I tell her that he is just out of town for work … but I think she knows something because some days she tells me she worries that I will be caught and taken away."