UK leader Keir Starmer warned far-right protesters on Sunday they would “regret” participating in England’s worst rioting in 13 years, as disturbances linked to the murder of three children earlier this week flared across the country for a fifth day.

Masked anti-immigration demonstrators smashed several windows at a hotel that has been used to house asylum seekers in Rotherham, South Yorkshire

Unrest related to misinformation about the mass stabbing last Monday in the northwestern English seaside town of Southport has impacted multiple towns and cities, with anti-immigration demonstrators clashing with police.

The violence is posing an early major challenge for Starmer, who was elected only a month ago after leading Labour to a landslide win over the Conservatives.

“I guarantee you will regret taking part in this disorder. Whether directly or those whipping up this action online, and then running away themselves,” Starmer said in a TV address.

He added that there was “no justification” for what he called “far-right thuggery” and promised to bring the perpetrators “to justice”.

Footage aired on the BBC showed rioters forcing their way into a Holiday Inn Express in Rotherham. They also pushed a burning bin into the building. It was not clear whether asylum seekers were inside.

In the northeastern English city of Middlesbrough, hundreds of protesters squared up to riot police carrying shields. Some threw bricks, cans and pots at officers.

The fresh disturbances came after more than 90 people were arrested on Saturday following skirmishes at far-right rallies in Liverpool, Manchester, Bristol, Blackpool and Hull, as well as Belfast in Northern Ireland.

Rioters threw bricks, bottles and flares at police – injuring several officers – looted and burnt shops, while demonstrators shouted anti-Islamic slurs as they clashed with counter-protesters.

The violence is the worst England has seen since the summer of 2011, when widespread rioting took place following the police killing of a mixed-race man in north London.

“We’re now seeing it (trouble) flooding across major cities and towns,” said Tiffany Lynch of the Police Federation of England and Wales.

Riots first flared in Southport on Tuesday night following Monday’s frenzied knife attack at a Taylor Swift-themed dance party in the northwest coastal city, before spreading up and down England.

‘Wake-up call’

They were fuelled by false rumours on social media about the background of British-born 17-year-old suspect Axel Rudakubana, who is accused of killing a six, seven, and nine-year-old, and injuring another 10 people.

Police have blamed the violence on supporters and associated organisations of the English Defence League, an anti-Islam organisation founded 15 years ago whose supporters have been linked to football hooliganism.

Agitators have targeted at least two mosques, and the UK interior ministry announced Sunday it was offering new emergency security to the Islamic places of worship.

The rallies have been advertised on far-right social media channels under the banner “Enough is enough”.

Participants have waved English and British flags while chanting slogans like “Stop the boats” – a reference to irregular migrants travelling to Britain from France.

Anti-fascist demonstrators have held counter-rallies in many cities, including Leeds where they shouted, “Nazi scum off our streets”, as the far-right protesters chanted, “You’re not English any more”.

Not all the gatherings have turned violent. A peaceful one in Aldershot, southern England, on Sunday saw participants hold placards that read “Stop the invasion” and “We’re not far right, we’re just right”.

“People are fed up with being told you should be ashamed if you’re white and working class but I’m proud white working class,” 41-year-old Karina, who did not give her surname, told AFP in Nottingham on Saturday.

Commentators have suggested that the demonstrators may feel emboldened by the political ascendancy of anti-immigration elements in British politics.

At last month’s election, the Reform UK party led by Brexit cheerleader Nigel Farage captured 14 per cent of the vote – one of the largest vote shares for a far-right British party.

Carla Denyer, co-leader of the left-wing Green party, said the unrest should be “a wake-up call to all politicians who have actively promoted or given in” to anti-immigration rhetoric.