British Prime Minster David Cameron says the police faced “a new and unique challenge” this week, as looting broke out at the same time in different places across the country.

He said police in London acknowledge they initially delayed too long before taking action to arrest rioters and looters, as he addressed Parliament Thursday. The violence first broke out after a protest over the death of a London man, Mark Duggan, who Cameron said was shot by police.

Cameron promised a thorough inquiry into Duggan’s death in Tottenham but said it could not be used as a justification for later violence.

The peaceful demonstration was “used as an excuse by opportunist thugs in gangs, first in Tottenham itself, then across London and then in other cities,” he said. “It is completely wrong to say there is any justifiable causal link.”

Cameron praised the bravery of individual officers in tackling rioters, but said: “What became increasingly clear earlier this week was that there were simply far too few police were deployed onto the streets. And the tactics they were using weren’t working.”

Police in Britain are being given more tools to tackle disorder, he told lawmakers, including greater powers to ask people suspected of causing trouble to remove face masks. Curfew powers will also be reviewed.

More than 1,200 people have now been arrested across the country, Cameron told lawmakers as he addressed an emergency session of Parliament, and if convicted they can expect to go to jail.

“Keeping people safe is the first duty of government,” he said. “The whole country has been shocked by the most appalling scenes of people looting, violence, vandalising and thieving.

“It is criminality pure and simple. And there is absolutely no excuse for it.”

Cameron said London would see a “surge” of 16,000 police officers — far more than the city’s usual policing levels — on its streets through the weekend.

A massive police presence seemed to have had its desired effect in Britain with authorities reporting no major outbreaks of violence on Thursday morning.

But much of the damage has already been done, with retailers losing more than £100 million ($161 million) in four nights of looting and violence, an analysis found.

READ MORE: CNN