The head of the Met Police and faith leaders joined a vigil on Monday night after the Finsbury Park terror attack.
Commissioner Cressida Dick was among hundreds who took part after a van hit worshippers near the Muslim Welfare House mosque and community centre.
Ramadan prayers took place on Monday after worshippers broke their fast, but leaders said it was quieter than usual.
Darren Osborne, 47, from Cardiff, has been held on suspicion of attempted murder and alleged terror offences.
His family members have said they are “”shocked” and “devastated”.
Mr Osborne’s mother, sister and nephew said in a statement: “We are massively in shock, it’s unbelievable. It still hasn’t really sunk in.”
They added that their “hearts go out to those who’ve been injured”.
The attack took place shortly after midnight on Sunday night, close to Muslim Welfare House on Seven Sisters Road.
The driver of the van was detained by bystanders before police arrived.
Nine people were taken to three London hospitals after a van struck pedestrians. Two were treated for minor injuries at the scene.
Several of the injured are believed to be seriously hurt.
Those who were injured had been helping a man who had collapsed. He later died but it is not clear if that was because of the attack.
Faith leaders addressed a crowd at the vigil outside nearby Finsbury Park Mosque. People from across the community had gathered in solidarity and to lay flowers.
After a short silence, chairman of the mosque Mohammed Kozbar said the attack was “on our families, on our freedom, on our dignity”.
The man who died was a father of six children, he said.
The Bishop of Stepney, Rt Rev Adrian Newman, said “an attack on one faith is an attack on us all”.
Ms Dick said the incident was “quite clearly an attack on Muslims”, and the community would now see more police, including armed officers, in the area, “particularly around religious establishments”.
Muslim worshippers then attended prayers at the mosque late into the night. At the scene, the BBC’s Simon Clemison said: “People came to prayer just as they would have done.
“It was pretty full – although one of the leaders of the mosque said it was quieter, he felt, quieter for one of the busiest times of Ramadan.”
He said there was positivity as people came from other parts of the capital to pray with the community.
But there were also some reservations amongst worshippers – ranging from the way the media reports events and on the community, to how politicians and decision-makers respond.
Some people in the area said the attacks left them “living in fear” as they went about their daily business.
Others said they wanted to show their support for the community – by taking flowers along to the site.
One, Caroline Bucknall, told the BBC she had lived locally for 20 years. She said she saw people of all faiths at the vigil and while everyone was sad, the community spirit was “very uplifting”.
‘Hate must not divide us’
The government is working to tackle hate crime and “all forms of extremism” the home secretary has said.
Writing in the Guardian, Amber Rudd said: “We must unite the might of community spirit and the full force of the law to ensure every person in the UK is protected. Let there be no doubt we will be tough on terror wherever it strikes. And last night’s attack was terrorism.”
She said this latest “attack on Britain” united everyone in grief and anger, adding: “It is vital, now more than ever, that we stand together and do not allow people who seek to use hate to divide us to succeed.”
Security Minister Ben Wallace said the suspect was not known to the security services, and was believed to have acted alone.
The BBC understands Mr Osborne grew up in Weston-super-Mare, Somerset, and has lived at more than one property in Cardiff. He is also believed to have lived in Swindon.
Police searches are being carried out in the Cardiff area.
Faith leaders from across Wales met at Dar Ul-Isra Mosque in the Welsh capital on Monday evening to make a human chain wall as an act of solidarity with the Muslim community.
The Finsbury Park attack is the fourth in the UK in three months, after incidents in Westminster, Manchester and on London Bridge.
Prime Minister Theresa May said the attack was “every bit as sickening” as the others. She visited Finsbury Park Mosque on Monday and held talks with faith leaders.
Labour leader and Islington North MP Jeremy Corbyn also visited the area, telling the BBC that “an attack on a mosque, an attack on a synagogue, an attack on a church is actually an attack on all of us”.
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