“Xinjiang has become an open-air prison — a place where Orwellian high-tech surveillance, political indoctrination, forced cultural assimilation, arbitrary arrests and disappearances have turned ethnic minorities into strangers in their own land,” Kumi Naidoo, secretary-general of Amnesty International, said in a video statement.

China’s mission to the United Nations in Geneva could not immediately be contacted for comment. Many Chinese government offices have closed in celebration of the Lunar New Year.

China initially responded to reports of mass incarceration of Muslims by issuing blanket denials, but its position changed after a United Nations panel monitoring religious equality expressed its alarm in August.

Defending its record at the Human Rights Council in November, China brushed aside allegations of mass detentions and abuses as politically motivated, presenting its camps as vocational training centers designed to improve the economic prospects and living standards of China’s minorities.

China has sought to reinforce the official narrative this year by taking small groups of diplomats and journalists on carefully arranged visits to Xinjiang, but journalists trying to make independent visits have faced obstacles.

The European Union said last week that a visit by three of its diplomats to sites carefully selected by the Chinese authorities had provided insight into China’s official thinking, “but does not invalidate the E.U.’s view of the human rights situation in Xinjiang, including in relation to mass detention, political re-education, religious freedom and sinicization policies.”

With their call for an international investigation on Monday, the human rights groups sought to ratchet up pressure for action not only by the United Nations but also by its member states, including members of the Organization of Islamic Cooperation, which remained conspicuously silent during November’s review of China’s record.