British Prime Minister Theresa May vowed Monday to fight extremism in all its forms after a white driver ploughed his van into a crowd of Muslims near a mosque.
It was the fourth terror strike in a tumultuous four months in Britain.
Ten people were injured in the attack which took place early Monday after evening prayers in Finsbury Park, north London.
One elderly man, who had collapsed just before the incident, was pronounced dead at the scene, but it is not yet known whether his death was directly linked to the attack.
May condemned the assault as "sickening", saying Britain's determination to fight "terrorism, extremism and hatred... must be the same, whoever is responsible".
The 47-year-old van driver was pinned down by people at the scene before being detained by police.
He was later arrested on suspicion of "the commission, preparation or instigation of terrorism including murder and attempted murder", the police said.
The Finsbury Park Mosque said the van "deliberately mowed down Muslim men and women leaving late evening prayers" at the mosque and the nearby Muslim Welfare House shortly after midnight.
Security Minister Ben Wallace told BBC radio that the suspect was "not known to us".
- Stepped up police presence -
London police chief Cressida Dick said the incident was "quite clearly an attack on Muslims" and promised a stepped-up police the presence near mosques as the holy month of Ramadan draws to a close.
Witness Abdiqadir Warra told AFP the van "drove at people" and that some of the victims were carried for several metres along the road.
"He was shouting: 'I want to kill all Muslims'," another witness, Khalid Amin, told BBC television.
Ten people were hurt, all Muslims, with eight requiring hospital treatment. Two were in a very serious condition, police said.
One Algerian man was among those injured, the north African country said.
Locals pinned down the driver and the imam of the Muslim Welfare House stepped in to stop him receiving a mob beating.
France and Germany quickly condemned the attack and Egypt's Al-Azhar institution, the leading authority in Sunni Islam, condemned it as "sinful".
"Al-Azhar affirms its total rejection of this terrorist, racist, sinful act, calling on Western countries to take all precautionary measures to limit the phenomenon of Islamophobia," it said in a statement.
US President Donald Trump's daughter Ivanka expressed solidarity with the worshippers in a tweet but her father has so far not commented.
- Community in shock -
May, who was heavily criticised for failing to meet survivors of a devastating fire in a London tower block last week, visited Finsbury Park Mosque where she met local faith leaders.
The use of a vehicle to mow down pedestrians drew horrifying parallels with this month's London Bridge attack, when three men drove a van into pedestrians before embarking on a stabbing spree -- an attack claimed by the Islamic State group -- and with another car and knife rampage near parliament in March.
This time the attacker deliberately targeted Muslims, according to the police.
"Over the past weeks and months, Muslims have endured many incidents of Islamophobia and this is the most violent manifestation to date," said Harun Khan, head of the Muslim Council of Britain, an umbrella body.
After the London Bridge attack, city mayor Sadiq Khan's office reported a 40-percent increase in racist incidents in the capital and a fivefold increase in anti-Muslim incidents.
Khan said it was a "horrific terrorist attack" aimed at "innocent Londoners, many of whom were finishing prayers during the holy month of Ramadan".
Mohammed Kozbar, chairman of the Finsbury Park Mosque, described the attack as "cowardly".
"Our community is in shock," he said, urging people attending prayers to remain vigilant.
- 'Extraordinary city' -
It was the third major incident in the capital this month, after the London Bridge attack and last week's devastating fire in the Grenfell Tower block, in which 79 people are thought to have died.
"This is an extraordinary city of extraordinary people," May said outside Downing Street after chairing an emergency government meeting.
"Diverse, welcoming, vibrant, compassionate, confident and determined never to give in to hate."
Last month, a suicide bomber blew himself up outside a pop concert in Britain's third city of Manchester, killing 22 people, many of them children.
The Finsbury Park Mosque was once a notorious hub for radical Islamists but has changed markedly in recent years under new management.
Its former imam, Abu Hamza, was jailed for life in New York on terrorism charges in 2015.
Despite the change in leadership and the focus on bolstering inter-faith relations, the mosque reported it had received a string of threatening emails and letters in the wake of the Paris attacks.
Some locals came onto the street in support of the mosque on Monday, carrying signs saying "We love our mixed community" and "Leave our Muslim neighbours alone".
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