The United States has ​denounced China’s treatment of its Uighur Muslims in unusually strong terms, adding to a growing list of disputes in increasingly turbulent relations between the two powers.

The secretary of state, Mike Pompeo, voiced alarm after a United Nations report described the mass internment of Uighurs under the pretext of preventing extremism in the western Xinjiang region where the minority group is concentrated.

“Hundreds of thousands and possibly millions of Uighurs are held against their will in so-called re-education camps where they’re forced to endure severe political indoctrination and other awful abuses,” Pompeo said in a speech on the state of religious freedom around the world.

“Their religious beliefs are decimated,” Pompeo said.

In a letter to Pompeo and the treasury secretary, Steve Mnuchin, and both Republican and Democratic members of Congress late last month called for sanctions on Chinese officials implicated in the internment of Uighurs.

Pompeo did not say whether the United States would take punitive measures but his remarks were striking for their tone, with ​Donald Trump’s administration putting human rights on the back seat in relations with allies such as Egypt and Saudi Arabia.

The Trump administration itself has faced criticism at home and abroad for its stance on Muslims, with the president as a candidate calling for a complete ban on Muslims entering the United States and, soon after taking office, barring entry to citizens of several Muslim-majority countries.

Pompeo also expressed concern about the fate of Christians in China, who he said had been targeted in a government crackdown.

The government, he said, has been “closing churches, burning Bibles and ordering followers to sign papers renouncing their faith”.

In an interview earlier in the week, Pompeo had described China as a greater threat to the United States than Russia, saying that Beijing was a “non-transparent government”.

“It treats our intellectual property horribly, it treats its religious minorities horribly,” he told Fox News.

China has rejected the findings of the UN Committee on the Elimination of Racial Discrimination.

Chinese foreign ministry spokeswoman Hua Chunying said last month that the report was “based on so-called information that is yet to be verified and has no factual basis”.

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