WASHINGTON/HONG KONG -- China on Wednesday condemned the U.S. Senate's passing of a bill in support of Hong Kong protesters, repeating a threat to retaliate with unspecified measures.

The upper chamber of Congress unanimously passed the Hong Kong Human Rights and Democracy Act, which requires the U.S. government to review annually whether the city's "one country, two systems" formula is functioning and calls for sanctions on those who abuse human rights in the former British colony.

"We urge the U.S. to take immediate actions to prevent the bill from becoming law and to stop interfering with Chinese domestic matters," China's Ministry of Foreign Affairs spokesman Geng Shuang told reporters in Beijing.

The city's government released a statement in which it expressed "deep regret" over the step, saying it will "harm the relations and common interests between Hong Kong and the U.S."

The House of Representatives approved its own version of the measure last month. Both pieces of legislation must be reconciled, then voted on in each chamber one last time before heading to the desk of President Donald Trump, who will have 10 days to sign the legislation into law or veto it, according to U.S. media.

The vote will complicate moves by the U.S. and China toward a preliminary agreement to end a trade war that is creating global economic uncertainty.

Peng Nian, a research fellow at Hainan University Belt and Road Research Institute, said Beijing is unlikely to change course on the ongoing trade talks to retaliate against the U.S. decision. He said this was because the negotiations have achieved interim results on key issues such as protection for intellectual property and purchases of agricultural products.

"While the foreign ministry is obliged to state its hard-line stance, China will not spoil the big deal for small gains," Peng said. The mainland scholar also noted that the U.S. is unlikely to take any concrete actions on Hong Kong because it is in Washington's interests to secure interim results.

Joshua Wong, a Hong Kong activist who was involved in lobbying the U.S. Congress to pass the bill, urged Trump to sign on the bill as soon as possible.

"Supporting Hong Kong should not be a matter of left or right... It should be a matter of right or wrong," Wong told the Nikkei Asian Review. "Human rights should never be overridden by a trade deal."

In an interview with Indianapolis-based radio host Tony Katz on Tuesday, Vice President Mike Pence noted that it will be difficult to sign a trade agreement with China if Beijing continues to encourage violence toward the Hong Kong protesters. "The president's made it clear it'll be very hard for us to do a deal with China if there's any violence or if that matter is not treated properly and humanely," Pence said.

In Hong Kong, more than 1,100 arrests have been made since Monday, and hundreds of demonstrators have been hospitalized due to a police siege of a university campus and related altercations.

The Hong Kong government on Wednesday made a request to the city's High Court for an anti-mask law to remain valid until the "final resolution" of its appeal against the court's ruling two days earlier, striking down the ban as unconstitutional. The government introduced the law in October to rein in escalating violence, but a group of pan-democratic lawmakers launched a legal challenge.

Also Wednesday, Beijing dismissed claims by a former employee of the U.K. consulate in Hong Kong who said that Chinese secret police tortured him while being detained in the mainland in August. "China expresses strong indignation over a string of wrong remarks concerning Hong Kong made by the British side," Geng said.

Anti-government protesters rest in the gymnasium at the besieged Hong Kong Polytechnic University in Hong Kong on Wednesday. © Reuters

China, which considers the human rights legislation as U.S. meddling in its internal affairs, has threatened "unspecified strong countermeasures" and has warned American lawmakers against pushing the bill.

Ma Ngok, a political-science professor at Chinese University of Hong Kong, said that the passage of the bill, in theory, offers a degree of constraint over Beijing's actions against Hong Kong, but its real impact remains to be seen.

The professor said while the bill has been a subject of discussion in the U.S. Congress for months, it did not stop Beijing from taking heightened measures to crack down on the protests.

"China should already have a very thorough evaluation on the effects of the bill," Ma said.

Additional reporting by Coco Liu and Dean Napolitano