The high commissioner and his staff have been in contact with the Chinese authorities for several months, but a letter he received from China over the weekend suggested that not all the individuals whose cases were raised by the United Nations were “guilty of criminal activities,” said a spokesman for the commission, Rupert Colville. He said the letter “did not address core issues.”

Mr. al-Hussein also expressed concern about five Hong Kong booksellers who disappeared beginning in October. Among the five, Lee Bo, a British citizen, vanished from Hong Kong at the end of December, and Gui Minhai, a Swedish citizen, disappeared in Thailand in October.

Both men later reappeared on the Chinese mainland. Mr. Lee was seen by his wife, whom he told that he was assisting a police investigation. Mr. Gui appeared on state television confessing to violating his probation in connection with a crime in 2003.

Mr. al-Hussein also took issue with the Chinese authorities over their treatment of a Swedish human rights activist, Peter Dahlin, who was the first foreigner to be detained in China on charges of endangering state security and who was later expelled after making a confession on state television.

“I find this method of ‘confession,’ extracted during incommunicado detention and publicized on national television, very worrying,” Mr. al-Hussein said. “It is a clear violation of the right to fair trial.”