David Cameron, the British prime minister, says he will recall parliament from its summer recess to address the unrest that has gripped the nation's capital and beyond.
Cameron pledged on Tuesday to "do everything necessary" to tackle the wave of rioting in London and other cities following three nights of violence on the streets of the capital.
"We've been discussing actions that we will be taking to help the police to deal with the disorder on the streets of London," Cameron said.
"We will do everything necessary to restore order to Britain's streets. Scenes of people attacking police officers and fire crews, this is criminality, pure and simple, this has to be confronted and defeated."
His comments came as reports surfaced that a 26-year-old man who was shot in a car in Croydon, south of London, had died in hospital, making him the first casualty during the violence.
"It's quite clear that we need much more police on our streets and more robust police action. All leave within the Met police has been cancelled," Cameron added.
"People should expect to see many more arrests in days to come, these people will see consequences of their actions."
But the violence appeared to spread later on Tuesday, with reports that youths had set fire to a retail store and smashed shop fronts in the northwestern city of Manchester, police said.
At least 525 people have been arrested as a consequence of the riots which escalated on Monday night, two days after a police station was attacked in the north London area of Tottenham following protests over the fatal shooting of a 29-year-old man, Mark Duggan, by police.
Britain's Independent Police Complaints Commission (IPCC) said on Tuesday that it had carried out ballistic tests on a handgun found at the scene, thought to have been owned by Duggan, and found that the gun had not been discharged.
The UK's Forensic Science Service is to carry out further tests on the weapon to verify this.
The IPCC's investigation also verified that the bullet found lodged in a police officer's radio handset was a standard issue police bullet, and that it showed signs consistent with being fired from a police gun, casting further doubt on claims that Duggan had fired the shot.
Rubber bullets considered
Meanwhile, London's Metropolitan Police said it would deploy 16,000 officers on the streets on Tuesday night - double the number on the streets on Monday night - to address any potential unrest.
As calls mounted for stronger measures, Deputy Assistant Commissioner Stephen Kavanagh said police would consider using baton rounds, rubber or plastic bullets.
Sporting events have been affected by the unrest, with England's football international against the Netherlands, which had been scheduled for Wednesday, the most high-profile cancellation.
Charlie Angela reports on the escalating violence in the UK
There were also incidences of looting and rioting in the cities of Birmingham, Liverpool and Bristol on Monday.
"There are pretty tough questions confronting the politicians," said Tim Friend, Al Jazeera's correspondent in London. "It will be concerning police and politicians greatly. Whether what's happening outside London has anything to do with the shooting [of Mark Duggan], is doubtful at the moment."
Government officials have branded the rioters criminals and said the violence would have no effect on preparations for the 2012 London Olympic Games - though television images of blazing buildings and rioting were likely to dent the capital's image.
"It was needless, opportunistic theft and violence, nothing more, nothing less. It is completely unacceptable," said Nick Clegg, the deputy prime minister, after visiting Tottenham on Monday.
He said the government stood "side by side with those people in those communities who utterly condemn the violence and the theft".
The administrators of a Facebook page, created in memory of Mark Duggan, posted this message: "Please we ask for this violence to stop. This isn't about Mark, it never was. His family never wanted nor thought any of this would happen.
"You people are using this as an excuse. If you had any respect, you would stop this before they bring in the Army, the whole world is looking."
The prime minister warned those who caused the violence and looting, "You will feel the full force of law, if you are old enough to commit the crime, you are old enough to face the punishment."
'Strong police response'
Reacting to the looting and violence spreading across the country, Ed Miliband, leader of the opposition Labour party, posted on his Twitter account: "Shocked by scenes in parts of London and Birmingham. We need strong police response to restore calm and for communities to work together."
Some activists and opposition politicians suggested that government spending cuts had driven disadvantaged and unemployed youths to violence.
But Mike Freer, conservative MP for Finchley and Golders Green, said that was "complete nonsense".
"These riots are about vandalism. To the best of my knowledge, we talked about cuts but most of them have not bitten yet. If Labour politicians really believe that, let's have a list of cuts that they think justified people turning to violence."
Others including David Lammy and Diane Abbott, MPs for the affected areas of Tottenham and Hackney, rejected the idea that the government's austerity drive should be blamed for the riots.
"Cuts don't turn you into a thief. What we saw was people thieving for hours," Abbott said.
Chukka Umunna, another Labour MP, said the violence in London was "totally opportunistic and utterly unacceptable".
"I think we have got to be very careful about seeking to draw general conclusions from a series of events around London to make some kind of historical judgement about what is going on," he added.
Cameron has resisted calls to slow the rate at which he is cutting the budget deficit in order to lessen the impact on youth services and other facilities. But he is likely to face new pressure to do more for poor districts of the capital.