The pair ran Rigby down in a car, then hacked him to death with knives and cleavers. Both were shot by police and arrested.

Analysts said the attackers wanted the publicity to inspire copycat attacks, and that they are already seeing an increase in chatter on extremist sites calling for such attacks. "We can see the tempo being raised," said Maajid Nawaz, a former jihadist now with the London-based anti-extremist Quilliam Foundation.

The killed soldier's anguished widow, Rebecca Rigby, spoke of her loss yesterday at his unit's headquarters.

"I love Lee and always will," she said, sobbing. "I am proud to be his wife and he was due to come up this weekend so we could continue our future together as a family."

London's Metropolitan Police put 1,200 extra officers on the street on Thursday, with patrols deployed at mosques and other religious sites, as far-right groups reacted to the killing near a barracks in south London by two self-proclaimed Muslim fighters.

Tell Mama co-ordinator Fiyaz Mughal, from Faith Matters, said three or four incidents were usually recorded a day. He said the surge in the number of incidents reported after Wednesday's killing reflected simmering resentment against Muslims that was unlikely to fizzle out.

"We are really concerned. When you see a wider picture of resentment and retribution, this is telling us it's an increasing problem," Mughal said. "Something is moving in a very disturbing direction."

A 43-year-old man was being questioned on Thursday on suspicion of attempted arson and possession of an offensive weapon at a mosque in Braintree, Essex. Another man was held on suspicion of racially aggravated criminal damage after Kent police were called to an incident at a mosque in Gillingham.

Graffiti attacks were reported on mosques in Bolton, where cars parked outside the building were also vandalised on Wednesday night, as well as in Cambridge on Thursday.

The incidents compiled by Tell Mama, which monitors news feeds and social media in addition to taking calls from the public, included seven incidents of Muslims being abused - with some spat at or threatened in the street. It logged threats against a further five mosques and dozens of other online threats.

On the "True British Patriots" Facebook page, people called for mosques in Watford, Hertfordshire, and Morden, south London, to be burned down.

The incidents came despite prompt condemnation of the murder by leaders of Muslim groups, including the Muslim Council of Britain and the Islamic Society of Britain.

The outrage was also condemned by individual Muslims, many of whom took to social networks to express their disgust. But Mughal warned: "I think the damage has been done."

He said his own address had been posted on Twitter, with users invited to shoot him.

In response to the heightened tension, he contacted mosques and police ahead of prayers yesterday amid fears that far-right groups may attempt to confront worshippers.

Hours after the murder, the English Defence League held a demonstration in Woolwich, during which its supporters engaged in running battles with police. The league has since said it will hold another gathering outside Downing Street on Monday, ostensibly to show support for British troops.

The league's Twitter account went into overdrive and thousands of people "liked" its Facebook page after the killing, although some people posting on it were challenging its ideology.

The British National Party announced its own demonstration in Woolwich a week today.

Prime Minister David Cameron and London Mayor Boris Johnson said the beliefs of the two men who killed the soldier were alien to Islam.

"This was not just an attack on Britain and the British way of life; it was also a betrayal of Islam and of the Muslim communities who give so much to our country," Cameron said.