China has experienced a "serious backsliding" in human rights, according to the US official handling bilateral talks on the issue on a visit to Beijing.

Assistant secretary of state Michael Posner said the Obama administration was deeply concerned about the deterioration, as he concluded two days of discussions in the Chinese capital.

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 runup to the talks.

"There is no question that the atmosphere [this time] was different, because the facts are different," Posner told a press conference at the US embassy in Beijing on Thursday. He added: "It was not a discussion where voices were raised, but it was was very much based on the facts and the facts are not good."

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

But he expressed particular concern about rights lawyers including Teng Biao, who has been missing for two months, and Chen Guangcheng , who has been unable to leave his home since his release from prison last year.

"[Teng] is exactly the sort of person society wants and needs to be available to represent clients who are on the margin," he said.

He also voiced concern for Gao Zhisheng, a lawyer who has not been seen for a year, and Liu Xia. Friends have been almost entirely unable to contact the poet since early October, shortly after her husband, jailed writer Liu Xiaobo, won the Nobel peace prize.

"That isn't to say there are not concerns about people going through the legal process. But the most unsettling and disturbing thing is when people simply disappear," added Posner, who leads on democracy, human rights and labour issues.

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

While critics have expressed concerns that the dialogue allows human rights to be marginalised, Posner said it was only part of the bilateral discussions on the issue and that human rights would also be on the agenda at the strategic and economic dialogue in the US next month.

China's foreign ministry spokesman Hong Lei said the dialogue had consisted of "frank and thorough exchanges on issues of mutual concern".

He added: "At the same time we oppose the United States using human rights to interfere in China's internal affairs."

Earlier, the state-run Global Times wrote in an editorial that most Chinese people "were disgusted" by outside pressure on human rights.

"As China is a sovereign nation, there is zero possibility of it allowing the US to dictate its political development," it added.

Police have released Zuoxiao Zuzhou, a rock star who is close friends with Ai Weiwei, according to friends. The musician was detained on Wednesday.

The Associated Press said Zuoxiao and a sports writer he was travelling with, Zhang Xiaodan, were released after questioning.

Several more friends and colleagues of the 53-year-old artist are still missing. 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.