HONG KONG — Hong Kong’s embattled leader, Carrie Lam, on Monday condemned violent clashes between a number of protesters and the police over the weekend, as her government scrambled to assert its authority after several increasingly volatile demonstrations and a surge in anti-police sentiment.

“We are here to thank our police officers for safeguarding Hong Kong’s safety at the front lines,” Mrs. Lam told reporters at a hospital where she was visiting several police officers who were injured in the clashes on Sunday. “They fulfilled their duties responsibly and were very professional and restrained, but they were intentionally attacked by people who I really think we can describe as rioters.”

On Sunday, tens of thousands of people attended a peaceful rally urging Mrs. Lam to fully withdraw a contentious bill and resign. By the evening, however, the demonstration had descended into a frenzied brawl between a small group of protesters and police officers in riot gear in a luxury shopping mall in Sha Tin, in the New Territories region of northern Hong Kong.

The clashes were the latest in a pattern that has emerged in Hong Kong in recent weeks in which mass rallies have ended in violent confrontations between a small group of mostly younger demonstrators armed with umbrellas and helmets and police officers wielding batons, pepper spray and shields.