Washington may sanction those involved in the arrest of over 50 people in Hong Kong and will send the US ambassador to the UN to visit Taiwan, Secretary of State Mike Pompeo said, drawing the threat of retaliation from Beijing.
Pompeo said he was also "appalled" by the arrest of an American citizen as part of Wednesday's crackdown and added: "The United States will not tolerate the arbitrary detention or harassment of US citizens."
Hong Kong police arrested 53 people in dawn raids on democracy activists on Wednesday in the biggest crackdown since China last year imposed a security law. Among those detained was American lawyer John Clancey, a source at his firm said.
Pompeo called the arrests an "outrage and a reminder of the Chinese Communist Party's contempt for its own people and the rule of law."
"The United States will consider sanctions and other restrictions on any and all individuals and entities involved in executing this assault on the Hong Kong people," Pompeo said.
He said it would also "explore restrictions against the Hong Kong Economic and Trade Office in the United States, and take additional immediate actions against officials who have undermined Hong Kong's democratic processes."
Further riling Beijing, Pompeo announced that Kelly Craft, Washington's UN ambassador, would visit Chinese-claimed and democratically run Taiwan, a highly symbolic trip as the island is not a UN member due to the objections of Beijing, which views Taiwan as a wayward province.
"Taiwan shows what a free China could achieve," he said.
Chinese Foreign Ministry spokeswoman Hua Chunying said Pompeo's comments represented a serious interference in the country's internal affairs, which China strongly condemned.
"China will take all necessary steps to resolutely safeguard its sovereignty and security interests," Hua told reporters.
"The United States must pay a heavy price for its mistakes."
The United Nations voiced alarm Thursday at the arrest of the 53 prominent figures in Hong Kong, urging their immediate release.
"We are deeply concerned about the arrests on Wednesday of 53 political activists, academics, former legislators, current district councilors, and lawyers in the Hong Kong Special Administrative Region, and we call for their immediate release," UN rights office spokeswoman Liz Throssel said in a statement.
"Yesterday's arrests were the latest in a series of detentions related to the exercise of fundamental freedoms, including the right to peaceful assembly, in Hong Kong," she said.