Uighur Muslims outside a mosque in Xinjiang - they make up 45% of the population in the region.
Nearly two dozen countries have signed a joint letter to the United Nations calling on China to end the mass detention of Uighur people.
Image: China calls this site in Dabancheng, Xinjiang, a 'vocational skills education centre'.
Reuters quoted a diplomat as saying China's delegation to the UN was "hopping mad" about the letter and is preparing its own response.
UN experts say around one million Uighur Muslims are being held in detention centres in the Xinjiang region, in northwest China.
The unprecedented letter also calls on China to allow experts, including the High Commissioner for Human Rights, "meaningful access" to the region.
China's foreign ministry said the letter "neglected the facts" and was a slander against China, an interference in its affairs and the politicisation of human rights. »
