Mike Pompeo prompted an angry response by branding China's re-education camps "the stain of the century."
Beijing is pursuing a vast campaign of sinicization in the western region of Xinjiang, where the majority of the population is Muslim.
"China was making a direct threat to me from my mother's voice. They're using my mom to silence me."
"The unabated oppression that the Uyghur community faces at the hands of China is a stain on the conscience of the world," Nancy Pelosi told Newsweek.
An editorial argued that China did not "have to be swayed by the whining" of the international community.
Beyond those who avoid alcohol, cigarettes and dancing, the government is reportedly concerned about individuals who encourage others to follow the teachings of the Quran.
"You don't need people's cooperation for us to be able to recognize their identity," said one researcher.
Last year, a senior Chinese official responded to the growing number of reports by describing the region's Muslims as "the happiest Muslims in the world."
"[Xinjiang] has avoided the fate of becoming 'China's Syria' or 'China's Libya.'"
China has been accused by the U.S. and others of repressing its Uighur Muslim minority, but ISIS has seldom featured Beijing in its propaganda.
As many as 1 million Chinese Muslims are believed to have been detained in the camps.
A human rights group says China is collecting data through medical checkups in Xinjiang, a move that further adds to controls in the Muslim-majority region.
The majority-Muslim region of Xinjiang has already been subject to increased government control in recent years.
The Uighurs, located in the restive region of Xinjiang, say Beijing crushes their religious freedoms.
The Chinese president is co-chairing a regional summit in Johannesburg on relations with Africa
An attack on a colliery in September killed 16 people, including five police officers
The few who have joined ISIS were inspired more by resentment of China than a global caliphate.
The measures are part of a broader push to step up security in response to violent unrest.
Chinese local authorities ban Islamic veils and beards amid ethnic tension with Xianjiang's muslim majority
A gang armed with knives had first attacked a police station and government offices in the town of Elixku