The UN Human Rights Council in Geneva will this week review China's progress since its last report in 2013.
China will be grilled over its mass detainment of Uighur minorities during a UN human rights review on Tuesday, with Washington leading demands for Beijing to come clean on how many people are held in a sprawling network of camps.
As many as one million ethnic Uighurs and other Muslim minorities are being kept in extra-judicial detention in China's fractious far western Xinjiang region, according to estimates cited by a UN panel.
The centres where they are thought to be detained have come under increasing scrutiny this year, with rights activists describing them as political re-education camps.
They say members of China's Muslim minorities are held involuntarily for transgressions such as wearing long beards and face veils.
"The Human Rights Council must send an unequivocal message to the Chinese government that their campaign of systematic repression in the Xinjiang Autonomous Region, including the arbitrary detention of up to one million people, must end," said Patrick Poon, China researcher at Amnesty International.
All 193 United Nations member states must undergo a periodic review by the UN Human Rights Council in Geneva.
China will present a report on its domestic human rights situation and on changes made since its last report in 2013, while diplomats from around the world will have the opportunity to ask questions - some of which have already been submitted.
One question by the US - which is leading demands for Beijing to come clean on the crackdown - says: "Can China clarify the basis for its apparent criminalization of peaceful religious practices as justification to detain people in these political 're-education' camps in Xinjiang, as well as which officials are responsible for this policy?"
Washington also wants Beijing to provide "the number of people involuntarily held in all detention facilities in Xinjiang during the past five years".
Britain has asked when China will implement a UN racial discrimination panel's recommendation that it "halt the practice of detaining individuals who have not been lawfully charged, tried, and convicted for a criminal offence in any extra-legal detention facilities".
The US and Germany have requested UN access to Xinjiang and Tibet to investigate allegations of mass detention and restrictions on religious freedoms.
'Like a prison'
Beijing previously denied the existence of such camps, but now defends them as "vocational education and training centres" where happy students study Mandarin, brush up on job skills, and pursue hobbies such as sports and folk dance.
Chinese officials say the facilities are part of efforts to combat terrorism, religious extremism and separatism in Xinjiang following unrest that left hundreds dead in recent years.
But an AFP investigation published in October showed that local authorities had bought gear for the centres including police batons, electric cattle prods, handcuffs, pepper spray, stun guns and razor wire.
The centres should "teach like a school, be managed like the military, and be defended like a prison", said one official document, quoting Xinjiang's party secretary Chen Quanguo.
"The Chinese government owes some answers to international questions about Xinjiang," Maya Wang, senior researcher at Human Rights Watch, told AFP.
The UN human rights review is a chance for countries to "focus their firepower on Xinjiang", though its effectiveness will depend on "whether or not there is commitment from the states to push for accountability," she added.
China will send a vice minister of foreign affairs, Le Yucheng, to head the delegation to the UN. Officials from Xinjiang, Tibet, Hong Kong and Macau will also attend the review.
"China is willing to carry out constructive dialogue with all sides in an open and honest spirit," Chinese foreign ministry spokesman Lu Kang told reporters on Friday.
Beyond Xinjiang, China will also come under scrutiny for other aspects of its human rights record.
Since President Xi Jinping took power in 2012, the Chinese government has cracked down on civil liberties and religious freedoms while ramping up digital surveillance.
In July 2017, dissident activist and Nobel Peace Prize winner Liu Xiaobo died of liver cancer while under police custody.
In 2015, more than 200 Chinese human rights lawyers and activists were detained or questioned in a sweep known as the "709" crackdown.
That year also saw five Hong Kong-based booksellers known for publishing gossipy titles about Chinese political leaders disappear before they resurfaced in mainland China.
"China opposes human rights politicization and 'double standards,' and upholds international fairness and justice," China said in a report submitted to the UN Human Rights Council for the review.
"No country's human rights situation is perfect. China still faces many difficulties and challenges in promoting and protecting human rights," it said.