“China is home to one of the worst human rights crises of our time; it is truly the stain of the century,” Pompeo told the final day of the international conference in Washington.
Pompeo said Chinese government officials had sought to discourage countries from attending the three-day event he has hosted.
“Is that consistent with the guarantee of religious belief that is found directly in the Chinese constitution?” he asked.
Pompeo, who said this week that more than 100 foreign delegations had been invited to the conference, congratulated countries which had defied Chinese pressure, while adding: “If you have declined to attend for the same reason, we take note.”
Pompeo did not name any of the countries and a State Department spokesman could not provide a figure.
“We know the Chinese government called countries specifically to discourage participation. We cannot prove the exact number they successfully impacted,” he said.
Pompeo’s remarks came a day after U.S. President Donald Trump met at the White House with victims of religious persecution from countries including China, Turkey, North Korea, Iran and Myanmar.
The Chinese government on Thursday rejected any suggestion that it abuses religious and human rights.
“In China this situation of so-called religious persecution does not exist,” Chinese foreign ministry spokesman Lu Kang told a news briefing in Beijing after the White House ceremony.
“We demand that the United States correctly view China’s religious policies and the status of religious freedom in China, and stop using the issue of religion to interfere in other countries’ affairs.”
U.S. Vice President Mike Pence, who has been a strong critic of China, was also due to address the Washington conference on Thursday morning.
Nearly two dozen nations at the U.N. Human Rights Council this month urged China to halt persecution of ethnic Uighurs in its western region of Xinjiang, where U.N. experts and activists say at least 1 million are held in detention centers.
The Trump administration has been weighing sanctions against Chinese officials over their policies in Xinjiang, including the Communist Party chief of the region, Chen Quanguo, but has held back amid Chinese threats of retaliation.
Relations between the United States and China are already tense over a tit-for-tat trade war, with the United States alleging that China engages in unfair trading practices.
(This story corrects word in fifth-paragraph quote to “reason” instead of “region”).
Reporting by David Brunnstrom and Lesley Wroughton; Editing by Susan Thomas