Washington may sanction those involved in the arrests of over 50 people in Hong Kong and will send the U.S. ambassador to the United Nations to visit Taiwan, Secretary of State Mike Pompeo said Thursday, drawing anger and a threat of retaliation from Beijing.

Pompeo said he was also "appalled" by the arrest of an American citizen in Wednesday's crackdown and added: "The United States will not tolerate the arbitrary detention or harassment of U.S. citizens."

Hong Kong police arrested 53 democracy activists in dawn raids Wednesday in the biggest crackdown since China imposed a security law last year opponents say is aimed at quashing dissent in the former British colony.