The police in cities across Britain were bracing on Sunday for the spread of far-right and anti-immigration protests, a day after dozens of people were arrested in another day of unrest after a stabbing in a northern town last week.

Protests in cities including Liverpool and Manchester descended into riots on Saturday, prompting a heavy police response in cities across the country. The National Police Chiefs’ Council, which represents law enforcement across Britain, has said that nearly 4,000 additional officers had been deployed to deter the violence.

“The police have our full backing,” Yvette Cooper, the British home secretary, said on Saturday. “I want everyone to be clear. Anyone who gets involved in criminal disorder, violent thuggery on our streets will have to pay the price.”

Tension has gripped some communities across the country after a stabbing rampage at a Taylor Swift-themed dance and yoga class on Monday in the town of Southport, near Liverpool, killed three young girls and injured many others. A 17-year-old suspect was later named.

Disinformation about the attacker’s identity spread quickly online, falsely identifying him as a migrant and fueling a violent, far-right riot in which a mosque was attacked and dozens of police officers were injured in Southport on Tuesday.

Unrest has since spread to other parts of Britain, with violent protests in Liverpool, Manchester, Leeds, Nottingham and other cities over the weekend. A protest was also held in Belfast, Northern Ireland, and also turned violent.