Keir Starmer has issued a stark warning to “far-right thugs”, saying they will regret taking part in violent disorder after riots escalated on Sunday, and a mob attempted to set fire to a hotel housing asylum seekers. The prime minister said the violent rioters targeting people because of their skin colour will be swiftly convicted, as he said “all right-minded people should condemn” the disorder. “Be in no doubt: those who have participated in this violence will face the full force of the law,” he said. “The police will be making arrests. Individuals will be held on remand. Charges will follow. And convictions will follow. I guarantee you will regret taking part in this disorder.” Speaking from Downing Street, he pledged to those feeling frightened about being targeted because of their race or religion that “this violent mob do not represent our country and we will bring them to justice”. Starmer will lead a Cobra meeting on Monday, as Labour, Conservative and Lib Dem politicians condemned the scenes of violent gangs attacking the Holiday Inn Express in Rotherham in South Yorkshire where asylum seekers were housed. A group of rioters in Middlesbrough in the north-east also walked through a residential area smashing the windows of houses and cars. At least 247 arrests have been made over the weekend across England and Northern Ireland, including in London, Hartlepool, Bristol, Belfast, Southport, Hull, Stoke-on-Trent and Liverpool, and some charges have been brought, with police warning of more to come once footage has been scoured. The violence is the worst mass disorder since the 2011 riots across England, with police dealing with 47 gatherings from the far right and counter-protesters on Saturday, and nine on Sunday. Chief constable BJ Harrington, the national lead for public order, told the Guardian a range of criminal offences were being investigated, from those committing violence on the streets, to those alleged to be whipping it up: “We are looking at a whole range of stuff. If we find there are people conspiring to commit violence, we will bring charges. “Social media is playing a large part, we are looking at that,” he said, adding it was being used in the “incitement and encouragement”. He said: “People in foreign countries are putting out disinformation.” Asked if that was a reference to the former EDL leader, Stephen Yaxley-Lennon who uses the name Tommy Robinson, the police chief said: “Tommy Robinson is one among many.” Harrington said, with 4,000 riot-trained officers pulled out of regular policing, “it is an obvious concern” that regular policing will suffer. Muslim leaders are warning their communities no longer feel safe, and the Home Office on Sunday offered new emergency security measures aimed at protecting mosques. It will involve fast-tracking the provision of security personnel available under a current scheme. The surge in extreme right-wing activity in the past week has led to a fivefold increase in threats to Muslims, such as rape and death, and a threefold increase in hate crime incidents, according to Tell Mama, a national monitoring group. It said Muslims in Britain have been left “terrorised” by the increase in extreme right-wing activity since Monday, which is directly linked to a large increase in anti-Islamic hate crimes. In a broadcast to the nation from No10, Starmer said those taking part, whether in person or “whipping it up online and then running away themselves”, would regret their actions. Asked whether he thought everyone taking part in the riots were “far-right thugs”, he said: “If you target people because of the colour of their skin or their face then that is far right and I’m prepared to say so. But it doesn’t matter what apparent motivation there is. This is violence, not protest. It doesn’t matter what the motivation is.” He hit out at the “marauding gangs intent on breaking the law or worse” that attacked a hotel housing asylum seekers in Rotherham, where the residents and staff were in absolute fear. “There is no justification, none, for taking this action and all right-minded people should be condemning this sort of violence,” he said. Starmer’s address from Downing Street is his second in three days, since the violence broke out earlier in the week. Diana Johnson, a Home Office minister, said the government would absolutely take a “nick them quick” approach to rioters, with plans for courts to sit longer hours to deal with suspects. The approach is aimed at taking rioters off the streets as quickly as possible and to act as a deterrent. The Police Federation warned this weekend that officers might not be able to attend other incidents as they scramble to respond to the widespread disorder, with outbreaks of violence in places including Liverpool, Manchester, Nottingham, Stoke and Belfast. Tiffany Lynch, the acting national chair of the Police Federation, said the clashes were “flooding across major cities and towns”. “We’re seeing officers that are being pulled from day-to-day policing to … go out there and essentially protect our communities,” she told BBC News. “But, while that’s happening, the communities that are out there that are having incidents against them – victims of crime – unfortunately, their crimes are not being investigated … We’re not going to be able to attend all of the incidents that are coming in on the 999s because we’re having to direct the priorities of what is happening on the streets.” Despite reports that the military could be brought in, Johnson said the police did not require extra resources. “There is no need to bring in the army and there has been no discussion about that,” she told BBC News. “We have been reassured that the police have the resources that they need to be able to deal with what’s happening at the moment,” Johnson said. “They have longstanding plans in place for mutual aid if they need to put extra police officers into certain parts of the country. We are certainly not hearing that things like 999 calls are not being answered.”