The US State Department called the action 'transnational repression'.

"The United States condemns the Hong Kong government’s issuance of new arrest warrants and bounties targeting six overseas democracy activists and the cancellation of passports for seven other activists, including some based in the United States," the Department said in a statement.

"We reject the Hong Kong government’s efforts to intimidate and silence individuals who choose to make the United States their home.  The United States does not waver in its advocacy for those who are targeted simply for exercising their right to freedom of expression," the statement said.

"The extraterritorial application of Hong Kong’s national security laws is a form of transnational repression that threatens U.S. sovereignty and the human rights and fundamental freedoms of people all over the world," the statement said.

The US State Department said the actions demonstrate Hong Kong authorities’ disregard for international norms and for the rights to freedom of expression and peaceful assembly. 

"We call on the Hong Kong government to stop using its national security laws to silence dissent," the statement said.

The Hong Kong Police recently announced cash rewards for information leading to the arrests of six  pro-democracy activists who are currently staying outside the region.

Among them is Tony Chung, the former leader of a pro-independence group who fled to the UK last year, reported BBC.

All the six people have been accused of violating the region's national security law.