The United States has expressed concern over China's "efforts to restrict and manipulate" the UN human rights chief's visit to the Xinjiang region, Secretary of State Antony Blinken says.
"The United States remains concerned about the UN High Commissioner for Human Rights Michelle Bachelet and her team's visit to the People's Republic of China (PRC) and PRC efforts to restrict and manipulate her visit," Mr Blinken said in a statement.
"We are concerned the conditions Beijing authorities imposed on the visit did not enable a complete and independent assessment of the human rights environment in the PRC, including in Xinjiang, where genocide and crimes against humanity are ongoing."
Washington had warned before Ms Bachelet made her long-planned visit to China that authorities would not grant her the necessary access to get a full assessment of the human rights situation.
Mr Blinken reiterated that stance, saying he was "troubled by reports that residents of Xinjiang were warned not to complain or speak openly about conditions in the region, [and] that no insight was provided into the whereabouts of hundreds of missing Uyghurs and conditions for over a million individuals in detention."
CEO of anti-slavery charity Arise, Luke de Pulford, told the ABC the UN visit sets a worrying precedent for future visits to authoritarian states
"It says to them, well, we've lowered the standards for China, why not also lower the standards for other places where there might be human rights abuses ongoing."
Mr Pulford said the visit "undermines" the work of researchers from around the world in raising the plight of Uyghurs and others in north-west China, calling it a "dereliction of duty on the part of the Office of the High Commissioner".
Ms Bachelet defended her visit earlier on Saturday, saying it was "not an investigation" but an opportunity to engage with the government.
She called on Beijing to avoid "arbitrary and indiscriminate measures" in its crackdown in Xinjiang and for them to review its counter-terrorism policies to ensure they comply with international human rights standards.
She started her China trip, the first by a UN Human Rights High Commissioner in 17 years, on Monday in the southern city of Guangzhou before heading to Xinjiang.
The UN human rights chief's access was limited as China arranged for her to travel in a "closed loop" — isolating people within a virtual bubble to prevent the spread of COVID-19 — with no foreign press.
Her office said last year it believed Uyghurs in Xinjiang had been unlawfully detained, mistreated and forced to work.
"I have raised questions and concerns about the application of counter-terrorism and deradicalisation measures under broad application, particularly the impact on the rights of Uyghurs and other predominantly Muslim minorities," she said during an online press briefing on Saturday.
China denies all accusations of abuse in Xinjiang.
Ms Bachelet said she raised with the Chinese government the lack of independent judicial oversight on the operation of the centres and allegations of the use of force, ill-treatment and severe restrictions on religious practice.
In 2019, Xinjiang governor Shohrat Zakir said all trainees had "graduated".
Human rights groups say more than 1 million people have been detained in indoctrination camps in the western Chinese region that aim to destroy the Uyghurs' Islamic culture and forcibly integrate them into China's Han majority.
Beijing denies the genocide allegations and says it is offering vocational training to reduce the allure of Islamist extremism.