China can't co-operate with the UN human rights office after it released a report criticising Beijing's policies against Uyghurs and other ethnic groups in western Xinjiang, a top Chinese diplomat said.

However, Chen Xu, China's ambassador to UN institutions in Geneva, distinguished between not working with the human rights office and co-operating with the world body overall.

Chen said the report issued last week – which said some rights violations under China's anti-terrorism policies could amount to crimes against humanity — offered up "groundless blame" of China's policies and practices.

Zumret Dawut, a Uighur from China's western Xinjiang region who was forcibly sterilised for having a third child, after being released from a Xinjiang detention camp. Photo / AP

"We cannot, on the one hand, conduct co-operation with the office, while at the same time it issued such a kind of assessment," Chen told UN Geneva press association ACANU. China believes the report "constitutes a threat" and cannot "conduct co-operation as if nothing happened", he said.

In the waning minutes of her last day in office on August 31, the office of Michelle Bachelet, then UN High Commissioner for Human Rights, issued a report accusing China of serious human rights violations against Uyghurs and other mostly Muslim ethnic groups. It called on the world community to give "urgent attention" to the situation in Xinjiang.

Human rights groups have accused China of sweeping a million or more people from the minority groups into detention camps - where many have said they were tortured, sexually assaulted and forced to abandon their language and religion.

China has repeatedly said the "assessment" was a fabrication cooked up by Western nations.

Chen said China — one of the five permanent members of the UN Security Council — will continue to work with the United Nations overall, calling the world body the "core" of international relations.

"We will continue the co-operation. But as I said, the office cannot represent the United Nations by delivering such an assessment, in such a nature," he said.

Chen also said China would take an "active part" in activities of the UN-backed Human Rights Council in its upcoming four-week session starting Monday.

The council works closely with the UN human rights office, which falls under the office of UN Secretary-General Antonio Guterres. On Thursday, the UN General Assembly chose Austria's Volker Türk as Bachelet's successor.