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.