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Leaked Communist Party documents and testimonies from former detainees and their relatives show that the centers for "re-education" are essentially prisons where detainees are forced to renounce Islam and express gratitude to the ruling party. They are subjected to indoctrination, torture and possibly forced labour, detainees said.

While Chinese authorities insist the detentions are a form of vocational training, classified documents recently leaked to a consortium of news organisations revealed a deliberate strategy to lock up Muslim minorities in large-scale, high-security detention camps for a minimum of one year even though they had not committed any crimes.



Xu Hairong, the Communist Party chief of Urumqi city, Xinjiang's capital, did not dispute the documents' authenticity. He said, however, that there was no such thing as "detention camps".



"The reports by The New York Times, the International Consortium of Investigative Journalists and other foreign media organisations are purely malicious attempts to smear and discredit Xinjiang's vocational education centers and its counter-terrorism and de-radicalisation efforts," Xu said.

Read more: Leaked documents reveal how Xinjiang camps work



Officials have repeatedly declined to say how many people are in the centres but insist the figure is far less than one million, but rights activists say the figure could be as high as three million.



Zakir said on Monday the number is "dynamic", adding that China would continue "training" for Xinjiang residents.



All those in the centers who were studying Mandarin Chinese, law, vocational skills and deradicalization have "graduated" and found stable employment, Zakir said, adding that others such as village officials, farmers and unemployed high school graduates continue to enroll on a rolling basis in programmes that allow them to "come and go freely".



Some former detainees have told the Associated Press they were forced to sign job contracts and barred from leaving factory grounds during weekdays, working long hours for low pay. Leaked documents suggest detainees are sent to a second level of labour camps after they "graduate", where they may engage in forced labour.



Many Uighurs abroad also say their relatives are in prison, not camps, after being sentenced on vague charges of extremism.



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