Prime Minister Theresa May said she would chair a meeting of the Cobra emergency committee later Monday. She said there has been no conflict among the groups in the past.
A police forensic tent erected at the scene in Finsbury Park, after a van collided with pedestrians.
The Metropolitan Police said eight people were taken to hospital and several were seriously injured in the incident which occurred on Seven Sisters Road after 12.20am.
One eyewitness who lives nearby told the BBC she saw people "shouting and screaming".
"Extra officers are on duty in the area to help reassure the local community", Police Commissioner Cressida Dick said.
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It's unclear whether the president could override those rules and order Rosenstein to fire Mueller. He said he would agree to dismiss Mueller only if there were a legitimate basis to do so.
Another witness, Hussain Ali, 28, said that while being restrained the suspect was protected by the people he is thought to have been targeting.
A witness, 38-year-old worshipper named Mehdi, told the Evening Standard that the van "tried to do a London Bridge thing", referring to the June 3 incident in which three male attackers deliberately crashed their van into pedestrians on the London Bridge. Rudd, who is in charge of government law enforcement, said: "Londoners have been hit with a series of attacksand have been nothing short of heroic". "In the meantime, I call on everyone to stand together against those who seek to divide us".
The Finsbury Park mosque has been associated with hate preacher Abu Hamza and a number of terrorists including shoebomber Richard Reid who attempted to detonate explosives on a flight from Paris to Miami in 2001.
Labour leader Jeremy Corbyn tweeted: "I'm totally shocked at the incident at Finsbury Park tonight".
"From the window, I started hearing a lot of yelling and screeching, a lot of chaos outside".
Police have not yet determined whether the fatality was a result of the van attack.
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I'm in charge of London fire brigade, and I was committing firefighters into something that was very unknown and very unsafe . He also appealed to anyone who may have escaped from the building, but has not yet come forward, to make themselves known.
Speaking to Buzzfeed News, he said: "This big van just came and went all over us".
Police have not offered any details about the cause of the crash. "I want to kill all Muslims".
He said he was also concerned about the lack of security measures around the building, and that congregations leaving prayers were not advised the safe way to enter and exit the mosque.
At this early stage of this investigation, no other suspects at the scene have been identified or reported to police, however the investigation continues. The Muslim Council of Britain has called the incident in London where a vehicle hit pedestrians earlier on Monday the most violent manifestation of Islamophobia to date.
However it is not known if the man's death is directly related to the attack, as he was already receiving first aid from the public at the scene.
On March 22, a man killed five people when he drove a auto into pedestrians on Westminster Bridge in London and stabbed a police officer.
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They examined the apartment where the fire started and determined "there is nothing to suggest the fire was started deliberately". May said after the meeting Saturday that there have been "huge frustrations" in the community as people tried to get information.
In May, 22 people were killed in an explosion at an Ariana Grande concert at the Manchester Arena.
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