China lashed out at the United States on Monday after Secretary of State Mike Pompeo called Beijing's treatment of the country's ethnic Uighur minority among “the worst stains on the world”.

Speaking at Kansas State University last week, Pompeo said Washington would use this month's UN General Assembly to rally support for the Uighurs, a mostly Muslim minority that has seen mass incarceration under the Chinese government.

“The lies of American politicians can't trick people around the world and will only further expose the purpose of their hidden political motives,” said Chinese foreign ministry spokeswoman Hua Chunying.

“We express our strong dissatisfaction and resolute opposition to these US officials who disregard the facts... and seriously interfere in China's internal affairs,” she told reporters at a press briefing in Beijing.

China has come under international scrutiny over its policies in the northwestern region of Xinjiang, where as many as one million Uighurs and other mostly Muslim minorities are being held in re-education camps, according to the 2018 findings of an independent UN panel.

After initially denying their existence, Beijing now defends the camps, which it calls “vocational education centres”, as a necessary measure to counter religious extremism and terrorism.

But former inmates and rights groups say individuals are subjected to political indoctrination and abuse.

A Kazakh businessman, who spent nearly two months in a camp, told AFP that people held there were forced to sing patriotic songs every morning and eat pork, a violation of Islam's religious restrictions.

In July, Chinese officials announced that “most” individuals have left the camps, without sharing figures — drawing scepticism and anger from the Uighur diaspora, many of whom remain out of contact with relatives and friends in Xinjiang.

“This may end up being one of the worst stains on the world of this century. It's of that magnitude,” Pompeo said on Friday.