The UN rights chief on Wednesday renewed her request to access China's Xinjiang region, where large numbers of the Uighur ethnic minority are reportedly being held in re-education camps.
In her annual address to the United Nations Human Rights Council, Michelle Bachelet said her office was seeking to "engage" with China on conditions in Xinjiang.
She also re-issued her requests for "full access to carry out an independent assessment of the continuing reports pointing to wide patterns of enforced disappearances and arbitrary detentions, particularly in the Xinjiang Uyghur Autonomous Region".
A UN panel of independent experts has said there are credible reports that nearly one million Uighurs and other Turkic language-speaking minorities are being held in Xinjiang.
Beijing at first denied the allegation, but later admitted putting people into "vocational education centres".
Xinjiang has long suffered from violent unrest, which China claims is orchestrated by an organised "terrorist" movement seeking the region's independence. It has implemented a massive, high-tech security crackdown in recent years.
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But many Uighurs and Xinjiang experts say the violent episodes stem largely from spontaneous outbursts of anger at Chinese cultural and religious repression, and that Beijing plays up terrorism to justify tight control of the resource-rich region.
Bachelet said she was confident that "stability and security in this region can be facilitated by policies which demonstrate the authorities' respect of all people's rights.