HONG KONG -- Hong Kong Chief Executive Carrie Lam on Monday condemned the violence that took place in the city's key commercial district and town bordering Shenzhen after another weekend of mass protests against a controversial extradition bill.
The march on Sunday was largely peaceful until a group of black-clad activists charged beyond the finish point and attacked Beijing's Liaison Office for the first time since the protests began over a month ago. They splashed black paint on the national emblem outside the building and sprayed graffiti on the exterior walls.
Lam, who had stayed out of public eye in the past few weeks, described these actions as "a flagrant challenge to China's sovereignty" and "deliberate test" of the "one country, two systems" principle under which the former British territory has been governed since it was handed over to Beijing in 1997.
"The SAR government will seriously follow up on the matter and investigate thoroughly according to the law," Lam said during a news conference on Monday, referring to the city's status as a special administrative region.
Beijing was quick to denounce the incident at the liaison office.
"These acts openly challenged the authority of the central government and touched the bottom line of the 'one country, two systems' principle," the government's Hong Kong and Macao Affairs Office said in a statement Sunday. Monday's front page of the Communist Party-run People's Daily newspaper denounced the protesters' behavior in similar terms.
U.S. President Donald Trump weighed in on the issue Monday saying Chinese President Xi Jinping has acted "very responsibly" with the protests in Hong Kong.
"I know it's a very important situation for President Xi," Trump said, when prompted by a reporter at an unrelated press briefing at the White House, adding that "China could stop them if they wanted" but instead has allowed the protests to go on for a long time.
"I hope that President Xi will do the right thing," he said.
At a news conference Monday, Foreign Ministry spokesperson Geng Shuang said Beijing will firmly support steps by Hong Kong authorities to protect central government institutions and punish "criminal elements."
Lam also said she had been concerned that the escalating clashes after recent marches could hurt Hong Kong's reputation as a safe place to do business.
Around midnight, police fired rubber bullets and tear gas to disperse remaining protesters in Central, the prime business district. By around 1 a.m., most protesters had left the scene.
But some protesters were unexpectedly attacked in Yuen Long, a town bordering Shenzhen, on their way back from the march. Some were chased and beaten by a group of men in white T-shirts in Yuen Long subway station. More than 40 people were injured and taken to hospital, including a lawmaker and a journalist. The police arrived half an hour after the attack and did not arrest anyone.
Some stores near the town center remain shut as rumors circulated online of more violence later on Monday.
Police Chief Stephen Lo said he would review the force's deployment of manpower, and said he would not tolerate any violence.
"We will pursue at all costs to bring the offenders to justice," he said during the same news conference.
Some 430,000 people attended Sunday's march, according to the organizer. Police put the figure at 138,000 at its peak.
Despite the suspension of the bill -- which would allow offenders to be extradited to mainland China to face trial -- protesters demand a formal retraction of the bill, and an independent probe into use of police force against them, among other things.