British Prime Minister Keir Starmer condemned what he described as "far-right thuggery" and said perpetrators would face the full force of the law after days of violent anti-immigration protests culminated in hotels being targeted.
Violent protests have erupted in towns and cities across Britain after three girls were killed in a knife attack at a children's dance class in Southport in northwest England last week.
The murders were seized on by anti-immigrant and anti-Muslim groups as misinformation spread that the suspected attacker was an immigrant and a radical Islamist. Police have said the suspect was born in Britain and are not treating it as a terrorist incident.
The protests have spread through cities across the country, including in Liverpool, Bristol and Manchester on Saturday, resulting in dozens of arrests as shops and businesses were vandalised and looted and several police officers were injured.
On Sunday, hundreds of anti-immigration protesters gathered by a hotel near Rotherham, northern England, which Britain's interior minister said was housing asylum seekers.
The protesters, many wearing masks or balaclavas, threw bricks at police and broke several hotel windows, a Reuters witness said, before setting a large bin close to the hotel on fire.
"I utterly condemn the far-right thuggery we've seen this weekend," Starmer said in a statement, adding it was criminal violence and not legitimate protest.
"Be in no doubt, those that have participated in this violence will face the full force of the law."
The National Police Chiefs' Council said 147 people had been arrested since Saturday evening and more would follow in the coming days.
Starmer, who took office a month ago after his Labour Party won a decisive election victory over the long-ruling Conservatives, said residents were in "absolute fear" from the "marauding gangs" in Rotherham.