Campaigners have warned that Chinese human rights lawyers remain under intense pressure, following the disappearance of another high-profile legal figure.

Li Fangping went missing on Friday after ringing his wife to say state security agents were waiting for him – just as lawyer Teng Biao returned home after a two-month disappearance. The US had singled out Teng's treatment and that of other missing lawyers in human rights talks the previous day. "The Chinese authorities are resorting to an old trick, the revolving-door approach – one in, one out – to create the impression that things are improving," said Renee Xia of the Chinese Human Rights' Defenders network.

"The crackdown on lawyers has not stopped," added Patrick Poon of the China Human Rights Lawyers' Concern Group.

He said he found this case particularly incomprehensible because while Li acted in high-profile cases he was careful not to discuss sensitive political issues.

Li's clients have included Zhao Lianhai, who founded a website about tainted baby milk after his son became sick, and activist and dissident Hu Jia.

Phelim Kine, Asia researcher for Human Rights Watch, said Li's disappearance suggested "a calculated effort to eviscerate China's besieged rights defence movement".

Li's wife told the South China Morning Post: "I believe [it] is related to his work. He has offended many people while helping the disadvantaged. I am not sure if state security officers are really the ones who have taken him away, or whether some gangsters are behind it."

Staff at Yangfangdian police station, where Li's wife has reported his disappearance, said the matter was confidential. A Beijing police employee said staff were not available to comment.

Asked about other missing lawyers last month, a foreign ministry spokeswoman said China protected its citizens' rights, including freedom of expression, but citizens had to obey the law and should not harm the public interest.

US assistant secretary of state Michael Posner last week said the Obama administration was deeply concerned about the deterioration in human rights in China, after concluding two days of discussions in Beijing. Dozens of dissidents, activists and lawyers have been detained, arrested or have vanished in the last two months. Both the US and China had made unusually strong comments on the issue in the run-up to the talks.

Posner said he had raised the high-profile case of detained artist Ai Weiwei, adding: "We certainly did not get an answer that satisfies."

Ai was detained at Beijing airport on 3 April. Officials say he is under investigation on suspicion of economic crimes, but police have not informed his family that they are detaining him and relatives say the case is retaliation for his social and political activism.

Posner said the US had also raised concerns about religious issues, the treatment of journalists and bloggers, and the situation for Tibetans and Uighurs.