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.
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.