Prime Minister Keir Starmer on Monday vowed "swift criminal sanctions" against far-right riots in several cities that have seen widespread damage and nearly 400 arrests, with fresh clashes breaking out in the evening.
Starmer convened ministers and police chiefs to discuss the unrest that has broken out since last Tuesday following a stabbing spree in which three children were killed in Southport, northwest England.
Mobs threw bricks and flares, attacked police, burnt and looted shops, smashed the windows of cars and homes and targeted at least two hotels housing asylum-seekers in a number of cities at the weekend.
The government will "ramp up criminal justice" to ensure that "sanctions are swift", Starmer told the media after Monday's meeting.
He said a "standing army" of specially-trained police was ready to be deployed to support local forces should any further riots break out.
Tensions flared again at several demonstrations across the country Monday evening, though less with less violence than at the weekend.
Sky News broadcast a tense standoff between far-right protesters and counter-demonstrators in the southwest city of Plymouth, punctuated by projectiles.
Police separating the rallies reported "violence towards officers in Plymouth" with one police van damaged.
"We are taking action against individuals who are intent on criminality. Arrests are ongoing," the police added on X.
Sky also reported that one of its vehicles was attacked by a man brandishing a knife in Birmingham.
- Hundreds of arrests -
The National Police Chiefs' Council (NPCC) said 378 people had so far been arrested, and that others would be "brought to justice".
"I want to reassure the public that a united and robust policing response is in place across the country and we are doing all we can to tackle this disorder," Chief Constable Gavin Stephens, NPCC chair, added.
Clashes erupted in Southport a day after three young girls were killed and five more children critically injured during a knife attack at a Taylor Swift-themed dance class.
False rumours initially spread on social media saying the attacker was a Muslim asylum seeker. The suspect was later identified as 17-year-old Axel Rudakubana, born in Wales. UK media reported his parents are from Rwanda, which has very few Muslims.
However, that has not stopped mosques from being targeted, with the government offering new emergency security to Islamic places of worship.
Arrests have been made nationwide as anti-immigration demonstrators and rioters face-off against police and counter-protesters, including groups of Muslims.
The prime minister on Sunday warned rioters they would "regret" participating in England's worst disorder in 13 years. Interior minister Yvette Cooper told the BBC on Monday that "there will be a reckoning".
Cooper also said that social media put a "rocket booster" under the violence, and Starmer stressed that "criminal law applies online as well as offline".
Police have blamed the violence on people associated with the now-defunct English Defence League, an anti-Islam organisation founded 15 years ago whose supporters have been linked to football hooliganism.
In some of the worst scenes on Sunday, masked rioters in Rotherham, northern England, smashed windows at a hotel that has been used to house asylum seekers.
At least 12 officers were injured, including one who was knocked unconscious, as they battled around 500 protesters with "far-right and anti-immigration views", South Yorkshire Police Assistant Chief Constable Lindsey Butterfield told media.
- Nationwide violence -
There were also disturbances in Bolton, northwest England, and Middlesbrough, northeast England, where mobs smashed windows of houses and cars, leading to 43 arrests.
Protesters there seized and broke a camera from an AFP crew. The journalists were not injured.
The violence is a major challenge for Starmer who led his Labour party to a landslide win over the Conservatives.
MPs from all sides have urged Starmer to recall parliament from its summer holiday to discuss the worst violence England has seen since 2011, when riots followed the police killing of a mixed-race man in London.
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 crossing the Channel to Britain from France.
Anti-fascist demonstrators have held counter-rallies in many cities.
At last month's election, the Reform UK party led by Brexit cheerleader Nigel Farage captured 14 percent of the vote -- one of the largest shares for a hard-right British party.