LONDON — British Prime Minister Keir Starmer said on Monday that a "standing army" of specialist police would be set up to deal with rioting and that the justice system would be ramped up to deal with hundreds of arrests after violent disorder rocked cities across the nation over the past week.

Starmer convened an urgent meeting after lawlessness that he blamed on far-right activists and misinformation on social media that whipped up anger over a stabbing rampage at a dance class that left three girls dead and many more wounded. False rumors spread online that the suspect was a Muslim and an asylum-seeker led to attacks on immigrants and Muslims.

"Whatever the apparent motivation, this is not protest. It is pure violence and we will not tolerate attacks on mosques or our Muslim communities," Starmer said. "The full force of the law will be visited on all those who are identified as having taken part in these activities." On Sunday, angry mobs attacked two hotels used to house asylum seekers, breaking windows and lighting fires before police dispersed the crowds and residents were evacuated. Dozens of police officers have been hospitalized for injuries in the past six days after being struck with bricks, bottles and large wooden posts.

Oliver Coppard, the mayor of South Yorkshire, where one of the hotels was attacked, attributed the violence to "far-right thugs." "As Keir said, as every decent person has said, I think these are far-right thugs who attacked some of the most vulnerable people in our communities and there is absolutely no excuse," Coppard told the BBC. "There can never be any excuse for trying to burn to death 200 of the most vulnerable people in our community." A Starmer spokesperson said no requests have been made to call in the army.

The Home Office, which is responsible for law and order, has offered mosques greater protection under a new "rapid response process" designed to quickly tackle the threat of further attacks on places of worship.

Starmer's spokesperson said after the meeting that social media companies have not done enough to prevent the spread of misinformation that has fueled far-right violence and vowed that anyone who stokes the disorder — online or on the streets — could face prison. Some of that false and misleading information has come from foreign states.

"The disinformation that we've seen online attracts amplification from known bot activity, which, as I say, can be linked to state-backed activity," the spokesperson said in a read-out of the meeting.