Pompeo reserved his toughest criticism for China in a keynote speech at a Vatican conference on religious freedom. The others were Cuba, Iran, Pakistan and Myanmar.

"When the state rules absolutely, it demands its citizens worship government, not God. That's why China has put more than one million Uighur Muslims ... in internment camps and is why it throws Christian pastors in jail," he said.

"When the state rules absolutely, God becomes an absolute threat to authority," he said.

China has been widely condemned for setting up complexes in remote Xinjiang that it describes as "vocational training centers" to stamp out extremism and give people new skills.

"Today we must gird ourselves for another battle in defense of human dignity and religious freedom. The stakes are arguably higher than they were even during the Cold War, because the threats are more diverse and more numerous," he said at the conference organized by the U.S. embassy to the Vatican.

Pompeo, who is due to meet Pope Francis on Thursday morning, later visited the Sistine Chapel and other parts of the Vatican museums.

His trip, which will also include a visit to his ancestral home in the rugged Abruzzo region northeast of Rome and stops in Montenegro, North Macedonia and Greece, has been overshadowed by an impeachment inquiry at home targeting President Donald Trump.

Democratic opponents have accused Trump of soliciting foreign interference in the 2020 U.S. election for his personal political benefit.

At issue is a July 25 phone call in which Trump asked Ukrainian President Volodymyr Zelenskiy to investigate Democratic Presidential candidate Joe Biden and his son Hunter in coordination with U.S. Attorney General William Barr and Trump's personal lawyer Rudy Giuliani.

Biden's son had served as a director for a Ukrainian gas company.

U.S. House Foreign Affairs Committee Chairman Eliot Engel and two other Democratic committee chairmen have accused Pompeo of "stonewalling" the impeachment inquiry, and called him a "fact witness" in the investigation, based on media reports that he had listened in on Trump's call with Zelenskiy.

Pompeo has not commented on Wall Street Journal report saying he took part in the phone call.

U.S. Secretary of State Mike Pompeo on Wednesday blasted China over its treatment of Uighur Muslims, during a Vatican conference taking place in the shadow of a political crisis back home.On Tuesday, he sternly objected to a move by the U.S. House of Representatives to obtain depositions from five current and former State Department officials as part of an impeachment inquiry.