Updated at 6:20 a.m. ET
LONDON - Britain will not let a "culture of fear" take over its streets, Prime Minister David Cameron insisted Wednesday, saying police have drawn up contingency plans to use water cannons if necessary to remove rioters from the streets.
Thousands of extra police officers on the streets kept a nervous London quiet after three nights of rioting, but looting flared in Manchester and Birmingham, where a murder probe was opened after three men were killed in a hit-and-run reportedly as they took to the streets to deter potential rioters.
"We will do whatever is necessary to restore law and order onto our streets," Cameron said in a somber televised statement. "Nothing is off the table" including water cannons, commonly used in Northern Ireland but never deployed in mainland Britain.
Cameron has recalled Parliament from its summer recess for an emergency debate on the riots Thursday.
An eerie calm prevailed in the capital Wednesday, where hundreds of shops were shuttered early or boarded up Tuesday night as a precaution, but unrest spread across England on a fourth night of violence by brazen crowds of young people.
Scenes of ransacked stores, torched cars and blackened buildings have frightened and outraged Britons just a year before their country is to host next summer's Olympic Games, bringing demands for a tougher response from law enforcement. Police across the country have made almost 1,200 arrests including 800 in London since the violence broke out in the capital on Saturday.
Armored vehicles and convoys of police vans backed up some 16,000 officers on duty almost triple the number who were out Monday night. The show of force seems to have worked there were no reports of major trouble in London on Tuesday night, although there were scores of arrests.
"What happened in London last night was, when community leaders and the police came together, there were significant arrests," said police deputy assistant chief constable Stephen Kavanagh. "Some looters were taken away before they got into doing anything, but it was that joint action that made the difference."
London courts worked through the night to process all those charged. Defendants appearing Wednesday included a 31-year-old primary school worker who admitted looting an electronics store, and a 15-year-old boy originally from Ukraine accused of throwing stones at police.
Meanwhile, militant online forums are abuzz with calls to Muslims in Britain to launch Internet campaigns in support of the British rioters and to urge them to topple the government.
Dozens of contributors on Wednesday suggested Muslims in Britain should flood social media websites, such as Facebook and Twitter, with slogans and writings inciting the British youth to continue rioting.
One contributor says the rioters should adopt slogans similar to those used by Arab protesters during the uprisings in the Middle East this year.
"The people want the killer of Mark Duggan punished" is suggested a reference to the British man whose death sparked the riots.
Another contributor says an Internet media attack is very important and that "chaos is useful to militants in London."
The violence has revived debate about the Conservative-led government's austerity measures, which will slash 80 billion pounds ($130 billion) from public spending by 2015 to reduce the country's swollen budget deficit.
Cameron's government has slashed police budgets as part of the cuts. A report last month said the cuts will mean 16,000 fewer police officers by 2015.
London mayor Boris Johnson like Cameron, a Conservative broke with the government to say such cuts are wrong.
"That case was always pretty frail and it has been substantially weakened," he told BBC radio. "This is not a time to think about making substantial cuts in police numbers."
Outside the capital, more looting was reported Tuesday night but not on the scale of Monday's violence in London.
Some 250 people were arrested after two days of violence in Birmingham, and police launched a murder investigation into the deaths of three men hit by a car. Residents said the dead men, aged 20 to 31, were members of Birmingham's South Asian community who had been patrolling their neighborhood to keep it safe from looters.
"They lost their lives for other people, doing the job of the police," said witness Mohammed Shakiel, 34. "They weren't standing outside a mosque, a temple, a synagogue or a church they were standing outside shops where everybody goes. They were protecting the community."
The killings have laid bare racial tensions underlying this week's riots in Birmingham, Britain's second-largest city and its most ethnically diverse. A fifth of the city's 1 million "Brummies" are Muslims, most commonly of Pakistani origin. About 7 percent are black, mostly Caribbean, in background.
While the riots that have swept England this week have involved looters of every creed and hue, the street anarchy also sometimes has exposed the racial fault lines that run beneath the poorest urban quarters.