The police admit they got their riot tactics wrong, the prime minister has said, as he announced measures to help homeowners and businesses.
David Cameron told MPs the riots in cities across England were "criminality pure and simple", but there were "far too few police" on the streets.
In an emergency recall of Parliament, he announced a crackdown on facemasks and a review on the use of curfews.
More than 1,500 arrests have been made since the unrest began on Saturday.
Mr Cameron told MPs that it had become clear there had been problems in the initial police response to the disorder.
"There were simply far too few police deployed on to our streets and the tactics they were using weren't working," said the prime minister
"Police chiefs have been frank with me about why this happened.
"Initially the police treated the situation too much as a public order issue - rather than essentially one of crime.
"The truth is that the police have been facing a new and unique challenge with different people doing the same thing - basically looting - in different places all at the same time."
Mr Cameron also set out a range of measures aimed at helping businesses and homeowners affected by the riots.
- To look at whether it would be right to stop people communicating via social media when "we know they are plotting violence, disorder and criminality"
- Plans to look at whether wider powers of curfew and dispersal orders were needed
- New powers for police to order people to remove facemasks where criminality is suspected
- Courts could be given tougher sentencing powers
- Landlords could be given more power to evict criminals from social housing
- Plans to extend the system of gang injunctions across the country and build on anti-gang programmes, similar to those in the US
- He said the government would meet the cost of "legitimate" compensation claims under the Riot Act and that the time limit would increase from 14 to 42 days
- A £10m Recovery Scheme to provide additional support to councils in making areas "safe, clean and clear"
- A new £20m High Street support scheme to help affected businesses get back up and running quickly
- Plans for the government to meet the immediate costs of emergency accommodation for families made homeless
The prime minister ruled out bringing in the Army, but said "every contingency" was being looked at - including whether the Army could undertake tasks that would free up more police for the front line.
He confirmed a reinforced police presence of 16,000 officers on the streets of London would remain in place over the weekend.
MPs debated the riots for more than seven hours - with most agreeing they were caused by criminals rather than protesters - and that there was no excuse for the actions of a lawless minority.
There was also universal praise for bravery of police - but some, including Home Secretary Theresa May, followed Mr Cameron's lead in criticising their tactics.
Mrs May said policing by consent was the British way, but robust action was needed.
Former Labour communities secretary Hazel Blears said police in her Salford constituency had briefly lost control of the streets - something that was "absolutely devastating" for the community.
More than 20 Labour MPs - led by shadow home secretary Yvette Cooper - have called on the government to reverse planned police cuts.
Labour leader Ed Miliband repeated their calls and urged the government to reconsider the plans.
He said: "The events of the last few days have been a stark reminder to us all that police on our streets make our communities safer and make the public feel safer.
"Given the absolute priority the public attaches to a visible and active police presence, does the prime minister understand why they would think it is not right that he goes ahead with the cuts to police numbers?
Mr Cameron insisted the cuts were "totally achievable" without any reduction in the visible policing presence and said that a "surge" of officers - as seen in recent days - would still be possible in future.
BBC political correspondent Iain Watson said Lib Dem sources had told him there was "absolute coalition unity" on reducing police budgets and the cuts would not be reversed.
Meanwhile, Commons Home Affairs Select Committee chairman Keith Vaz has told the BBC its members have voted unanimously to hold an inquiry into the causes of the riots.
It will also look at the role of social networking, the police response and police resources.
In other developments:
- A man is arrested over an attack on a Malaysian student who was attacked by rioters in East London and mugged by people who had initially appeared to be helping him
- More than 100,000 people have signed an online petition calling for anyone convicted of taking part in the riots to lose any benefits they receive - becoming the first to be considered for a Commons debate
- Up to 250 officers were sent from Scotland to help police in the Midlands and North of England deal with rioting and disorder
- Police in London say they have more than 100 arrest warrants to work through "in the coming hours and days"
- The government launches a website with advice to the public on how to cope with the unrest
- Saturday's Premier League match between Tottenham and Everton at White Hart Lane has been postponed
Meanwhile, the Met Police have made 1,009 arrests and 464 people have been charged.
West Midlands Police have also arrested 389 people and 147 have so far been arrested in Manchester and Salford.
Courts sat through the night in London, Manchester and Solihull to deal with people arrested during the four nights of disturbances.
Mr Cameron told the Commons that anyone convicted of violent disorder would be sent to prison.
But Met Deputy Assistant Commissioner Stephen Kavanagh said some officers had voiced disappointment at the sentences handed out so far.
Mr Kavanagh added that there had since been "constructive conversations" between the home secretary, the Met commissioner and the courts.
The prime minister also offered his condolences to the families of Haroon Jahan, Shazad Ali and Abdul Musavir, who died when they were hit by a car in Birmingham on Tuesday night.
He called their deaths "truly dreadful".
Two youths and a man have been arrested on suspicion of murder, while a 32-year-old man arrested on Wednesday has now been been bailed.
The riots first flared on Saturday after a peaceful protest in Tottenham over the fatal shooting of Mark Duggan, 29, by police.
Mr Duggan's death is being investigated by the Independent Police Complaints Commission.