David Cameron has insisted yesterday's killing in Woolwich was a betrayal of Islam, amid concerns about a wave of anti-Muslim violence.
A 100-strong group of English Defence League (EDL) members marched in the nearby area last night and British National party (BNP) leader Nick Griffin took to Twitter to call for a protest – 'United against Muslim terror' – for this Saturday.
Meanwhile, Kent police confirmed they are investigating reports of criminal damage at a Mosque in Gillengham, while Essex police said they had arrested a 43-year-old man following reports he was in possession of a knife outside a prayer centre in Baintree.
Neither incident has been officially linked to the Woolwich attack.
"This was not just an attack on Britain. It was a betrayal of Islam and the Muslim communities who give so much to our country," Cameron said outside Downing Street this morning.
"This terrorism has taken more Muslim lives than any other religion. Confronting extremism is a job for us all."
"This country will be resolute in its stand against violence extremism. This view is shared by every community in our country."
London mayor Boris Johnson said added: "It is completely wrong to blame this killing on Islam.
"The fault lies with the warped mindset of those who did it and for the sake of the victim and his family the killers need to be brought to justice."
This morning's high-level Cobra meeting involved a discussion about community cohesion. The "strength and unity of response from Muslim community leaders" was recognised and commended by ministers and others around the table, according to government officials.
The moves by the far-right to drum up hatred towards Muslims appeared to be a specific goal of the two men who conducted the killing yesterday.
One said to a passer-by: "We want to start a war in London tonight."
Hours later, men wearing EDL face masks with a St George's Cross gathered near Woolwich Arsenal station gathered for protests organised on social media.
Hundreds of police in riot gear surrounded them. Missiles were thrown and there were outbreaks of disorder, but the demonstration did not enflame any further.
EDL leader Tommy Robinson said: "They're chopping our soldiers' heads off. This is Islam. That's what we've seen today. They've cut off one of our army's heads off on the streets of London."
A spokesperson from the Muslim Council of Britain (MCB) said: ""This is a truly barbaric act that has no basis in Islam and we condemn this unreservedly.
"This action will no doubt heighten tensions on the streets of the United Kingdom. We call on all our communities, Muslim and non-Muslim, to come together in solidarity to ensure the forces of hatred do not prevail."
Section 60 of the Public Order Act was used to allow officers to stop and search individuals.