HONG KONG: China has issued a protest over remarks the US ambassador-at-large for international religious freedom made criticising Beijing's policies toward Muslim and Tibetan Buddhist minorities and saying the country was "at war with faith."

The foreign ministry's office in Hong Kong said the speech Sam Brownback gave Friday "slandered" China's religious policies. It said it had registered its dissatisfaction Saturday with the US Consulate in the semi-autonomous Chinese region, where the speech was given.

China's constitution and laws protect freedom of religion and critics should "cease their slander of China's policies on religion and the situation with freedom of faith and cease using religious issues to interfere in China's internal affairs," the office said in a statement.

US officials and UN experts say China is believed to be holding 1 million Uighurs, Muslims and members of another majority Muslim ethnic groups in political education camps in Xinjiang. The US and other governments have criticised the crackdown.

The Chinese government says those camps are vocational training centres designed to rid the region of extremism.

Brownback said President Donald Trump's administration is "deeply concerned and considered it a deliberate attempt by Beijing to redefine and control these Muslim minority groups, (their) identity, culture and faith."

He urged Beijing to grant free access to the camps to investigate claims of abuse of inmates.

More generally, Brownback said, China is "at war with faith."

"It's a war they will not win," he said. "The Chinese Communist Party must hear the cry of its people for religious freedom."

Brownback was expected to meet local religious leaders and religious studies students and instructors while in Hong Kong. The territory enjoys the freedom of speech and religion far beyond that in mainland China, where the officially atheist government keeps tight control over any potential challenges to its authority.

Brownback, the former governor of Kansas, was due to travel to Taiwan for a regional meeting on religious freedom Monday.

In his speech, the Catholic conservative called on China to release Wang Yi and John Cao Sanqiang detained pastors in the "underground" church that operates independently of official government agencies.