"Nowhere is religious freedom under assault more than in China," Pompeo told a symposium hosted by the U.S. Embassy to the Holy See, saying the Chinese Communist Party was looking to "to snuff out the lamp of freedom on a horrifying scale."
Pompeo, an evangelical Christian who has portrayed himself as a champion of religious rights, denounced Beijing's treatment of its Uighur Muslim minority, and said all religious groups faced repression.
China has consistently defended its human rights record and has denied any mistreatment of Uighurs.
Pompeo is due to hold talks on Thursday with Cardinal Pietro Parolin, the Vatican's top diplomat. Pope Francis saw Pompeo when he came to Italy last year but no such meeting is scheduled this time around.