The UN says it is alarmed by reports of the mass detention of Uighurs in China and called for the release of those held on a counter terrorism "pretext".
It comes after a UN committee heard reports that up to one million Muslim Uighurs in western Xinjiang region, were held in re-education camps.
Beijing has denied the allegations but admitted that some religious extremists were being held for re-education.
China blames Islamist militants and separatists for unrest in the region.
During a review earlier this month, members of the United Nations Committee on the Elimination of Racial Discrimination said credible reports suggested Beijing had "turned the Uighur autonomous region into something that resembles a massive internment camp".
China responded that Uighurs enjoyed full rights but Beijing made a rare admission that "those deceived by religious extremism... shall be assisted by resettlement and re-education".
Xinjiang has seen intermittent violence - followed by crackdowns - for years.
What does the UN say?
The UN body on Thursday released its concluding observation, criticising the "broad definition of terrorism and vague references to extremism and unclear definition of separatism in Chinese legislation".
The committee called on Beijing to:
- End the practice of detention without lawful charge, trial and conviction;
- Immediately release individuals currently detained under these circumstances;
- Provide the number of people held as well as the grounds for their detention;
- Conduct "impartial investigations into all allegations of racial, ethnic and ethno-religious profiling".
What is China accused of?
Human rights groups including Amnesty International and Human Rights Watch have submitted reports to the UN committee documenting claims of mass imprisonment, in camps where inmates are forced to swear loyalty to China's President Xi Jinping.
The World Uyghur Congress said in its report that detainees are held indefinitely without charge, and forced to shout Communist Party slogans.
It said they are poorly fed, and reports of torture are widespread.
Most inmates have never been charged with a crime, it is claimed, and do not receive legal representation.
The latest UN statement comes amid worsening religious tensions elsewhere in China.
In the north-western Ningxia region, hundreds of Muslims have been engaged in a standoff with authorities to prevent their mosque from being demolished.
Who are the Uighurs?
The Uighurs are a Muslim ethnic minority mostly based in China's far-western region of Xinjiang. They make up around 45% of the population there.
Xinjiang is officially designated as an autonomous region within China, like Tibet to its south.
Reports that more and more Uighurs and other Muslim minorities are being detained in Xinjiang have been circulating for some months.
China is said to carry out the detentions under the guise of combating religious extremism.