Friday's statement from Pompeo, the top U.S. diplomat, went further than the State Department's warning to China a day earlier and showed how rapidly the world has reacted to news that Beijing is set to impose new national security legislation on Hong Kong, despite last year's pro-democracy protests in the territory.
"Given that the protests and their intensity have been driven by Beijing's erosion of promised freedoms, Beijing's direct imposition of a security law would clearly enflame the population", said Victoria Tin-bor Hui, an associate professor of political science at the University of Notre Dame who has been following the protests.
Pompeo said that Beijing's latest moves would "inevitably" influence the State Department's decision.
Chinese foreign ministry spokesman Zhao Lijian held a regular daily news conference in Beijing, saying that national security in Hong Kong was "purely" an internal affair.
These attempt have usually been met with widespread distrust of China's Government.
But six months of mass protests against closer legal ties to the mainland appear to have convinced China's leader, Xi Jinping, that winning local support is futile.
So, he finally made his move.
He said democracy activist Joshua Wong (黃之鋒) told him on the phone Friday that as a result of the Chinese law proposal, many of his friends and colleagues in Hong Kong now feared for their lives.More news: Osaka named richest female athlete in the world
Hong Kong's government said it would co-operate with Beijing to enact the law, adding it would not affect the city's freedoms.
The Government also wants to prohibit foreign political organisations or bodies from conducting political activities in Hong Kong or having links with overseas bodies.
By including foreign interference under national security, the law could also curb worldwide lobbying by pro-democracy activists.
A return of violent protests would push the city's already weakened economy into a downward spiral, prompting multinational companies to reconsider their presence in Asia's financial hub and Washington to review its policy of granting the territory more advantageous trade conditions than mainland China, Tsang warned.
Others potentially in the firing line include the thousands of protesters seen at rallies past year carrying signs advocating Hong Kong independence or booksellers who publish gossipy titles about Chinese political leaders.
Beijing tried to introduce a similar law in 2003 but shelved the initiative due to mass protests.
Instead, it has chosen what he called a "worse option" by proposing the NPC enact a national security law for the city. "It is a complete dishonour of promises made under the Sino British Joint Declaration, as well as all the promises made by the Chinese government to us and the world", she said.
He wrote on Twitter: "Appalling power grab by China over Hong Kong".More news: Trump calls on churches to reopen this weekend
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"This is the end of Hong Kong, this is the end of "One Country, Two Systems", make no mistake about it", Civic Party lawmaker Dennis Kwok told reporters.
Pro-democracy activists had said they feared "the end of Hong Kong" if China brought the new security law.
"But the other is to draft it up in Beijing and instruct the Hong Kong Government to put it into effect".
"This is nearly like a nuclear option, which once you use it, everyone will get hurt, and it will be very hard to build Hong Kong back up again", Kwok told the conservative Heritage Foundation by videoconference. The United States should stand up for its democratic values and stand with Hong Kong's citizens.
The millions-strong, often violent protests a year ago sparked by a controversial extradition law shocked the Chinese leadership and in recent months, Chinese officials have unequivocally ordered the city to enact legislation to bar subversion, separatism, and foreign interference to plug the national security "loopholes" that threaten the country's stability.
It's a subtle change on paper, but with historic ramifications for the people of Hong Kong.More news: Pakistan not using England tour as leverage, says PCB CEO