The United States on Friday 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.

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 Treasury Secretary Steve Mnuchin, 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.

Even so, the remarks were striking for their tone, with President Donald Trump's administration putting human rights on the back seat in relations with allies such as Egypt and Saudi Arabia.