"The extraterritorial targeting of Hong Kongers who are exercising their fundamental freedoms is a form of transnational repression," Rubio said in a statement.

"We will not tolerate the Hong Kong government's attempts to apply its national security laws to silence or intimidate Americans or anyone on US soil."

Hong Kong police on Friday announced bounties for information leading to the arrest of 19 overseas activists, accusing them of national security crimes.

Police said the activists were involved in what they called the "subversive" Hong Kong Parliament -- a pro-democracy non-governmental organization established in Canada.

A reward of HK$200,000 ($25,500) each was offered for 15 of the activists, while the four others were already wanted for HK$1 million, the statement said.

"With this new round of arrest warrants and bounties, the Hong Kong government continues to erode the autonomy that Beijing itself promised to the people of Hong Kong following the 1997 handover," Rubio said.

"Freedom of speech and political discourse are core American values, which the Trump administration will continue to defend."