China warned the US that it was ready to take "firm countermeasures" after President Donald Trump signed a law supporting pro-democracy protesters.
"The nature of this is extremely abominable, and harbours absolutely sinister intentions," the Chinese foreign ministry said in a statement.
It added that the legislation sent the wrong signal to demonstrators and "clearly interfered" with the city's internal affairs.
On Wednesday, Trump signed into law congressional legislation that supported the protesters despite objections from Beijing.
The new legislation will require the US to annually confirm that Hong Kong's special freedoms are being maintained by China.
Anti-government protests have roiled the city for six months, with more than 5,800 people arrested for violent outbreaks.
Russian drone strike kills 12 miners in Ukraine
Five-year-old boy returns to Minnesota after ICE release
Reopening of Gaza's Rafah crossing expected Monday
Winter storm death toll in United States reaches 90
Pakistan says 145 militants killed after attacks in Balochistan
Israeli strikes kill 26 in Gaza, health officials say
US government starts likely brief shutdown as House fails to approve deal
Thousands demonstrate in Minnesota and across US to protest ICE
