BEIJING (AP) — China reacted furiously Thursday to President Donald Trump’s signing of two bills aimed at supporting human rights in Hong Kong, summoning the U.S. ambassador to protest and warning the move would undermine cooperation with Washington.

Hong Kong, a former British colony that was granted semi-autonomy when China took control in 1997, has been rocked by six months of pro-democracy demonstrations.

Thousands of pro-democracy activists crowded a public square in downtown Hong Kong on Thursday night for a “Thanksgiving Day” rally to thank the United States for passing the laws and vowed to “march on” in their fight.

Trump’s approval of the bills was not unexpected. Neither was the reaction from Beijing. Analysts say the bills are mostly symbolic. But the clash comes at a sensitive time and could upset already thorny trade talks between the nations.

Chinese Vice Foreign Minister Le Yucheng told U.S. Ambassador Terry Branstad that the move constituted “serious interference in China’s internal affairs and a serious violation of international law,” a Foreign Ministry statement said.

Republican lawmakers have been outspoken in favor of the bills.

“Know this, Chairman Xi: Americans despise tyrants and stand in solidarity with Hong Kong. The whole world has seen both the courage of Hong Kongers and the brutality of your Chinese Communist Party,” Sen. Ben Sasse, R-Neb., said in a statement issued after Trump signed the bills. “As long as freedom-seekers fill the streets of Hong Kong, the American people will take their side.”

This report includes material from the Washington Post.