LONDON (AP) — Britons swept up, patched up and feared further violence Tuesday, demanding police do more to protect them after three nights of rioting left looted stores, torched cars and blackened buildings across London and several other U.K. cities.

Police said they were working full-tilt, but found themselves under attack — from rioters roaming the streets, from a scared and worried public, and from politicians whose cost-cutting is squeezing police numbers ahead of next year’s Olympic Games.

London’s Metropolitan Police force vowed an unprecedented operation to stop more rioting, flooding the streets Tuesday with 16,000 officers, nearly three times Monday’s total.

Although the riots started Saturday with a protest over a police shooting, they have morphed into a general lawlessness that police have struggled to halt with ordinary tactics. Police in Britain generally avoid tear gas, water cannons or other strong-arm riot measures. Many shops targeted by looters had goods that youths would want anyway — sneakers, bikes, electronics, leather goods — while other buildings were torched apparently just for the fun of seeing something burn.

Police said plastic bullets were “one of the tactics” being considered to stop the looting. The bullets were common in Northern Ireland during its years of unrest but have never before been used in mainland Britain.

But police acknowledged they could not guarantee there would be no more violence. Stores, offices and nursery schools in several parts of London closed early amid fears of fresh rioting Tuesday night, though pubs and restaurants were open. Police in one London district, Islington, advised people not to be out on the streets “unless absolutely necessary.”

“We have lots of information to suggest that there may be similar disturbances tonight,” Commander Simon Foy told the BBC. “That’s exactly the reason why the Met (police force) has chosen to now actually really ‘up the game’ and put a significant number of officers on the streets.”

The riots and looting caused heartache for Londoners whose businesses and homes were torched or looted, and a crisis for police and politicians already staggering from a spluttering economy and a scandal over illegal phone hacking by a tabloid newspaper that has dragged in senior politicians and police.

“The public wanted to see tough action. They wanted to see it sooner and there is a degree of frustration,” said Andrew Silke, head of criminology at the University of East London.

London’s beleaguered police force called the violence the worst in memory, noting they received more than 20,000 emergency calls on Monday — four times the normal number. Scotland Yard has called in reinforcements from around the country and asked all volunteer special constables to report for duty.

Police launched a murder inquiry after a man found with a gunshot wound during riots in the south London suburb of Croydon died of his injuries Tuesday. Police said 44 officers and 14 members of the public were hurt, including a man in his 60s with life-threatening injuries.

So far more than 560 people have been arrested in London and more than 100 charged, and the capital’s prison cells were overflowing. Several dozen more were arrested in other cities.

Violence first broke out late Saturday in the low-income, multiethnic district of Tottenham in north London, after a protest against the fatal police shooting of Mark Duggan, a 29-year-old father of four who was gunned down in disputed circumstances Thursday.

Police said Duggan was shot dead when officers from Operation Trident — the unit that investigates gun crime in the black community — stopped a cab he was riding in.

The Independent Police Complaints Commission, which is investigating the shooting, said a “non-police firearm” was recovered at the scene, but that there was no evidence it had been fired — a revelation that could fuel the anger of the local community.

An inquest into Duggan’s death was opened Tuesday, though it will likely be several months before a full hearing.

Duggan’s death stirred memories of the bad old days of the 1980s, when many black Londoners felt they were disproportionately stopped and searched by police. The frustration erupted in violent riots in 1985.

Relations have improved since then but tensions remain, and many young people of all races mistrust the police.

Others pointed to rising social tensions in Britain as the government slashes 80 billion pounds ($130 billion) from public spending by 2015 to reduce the huge deficit, swollen after the country spent billions bailing out its foundering banks.