A man has died and 10 people were injured after a van was driven into a group of worshippers outside a north London mosque.
The vehicle hit pedestrians near Finsbury Park Mosque as they left Ramadan night prayers around midnight.
Police are treating the incident, on Seven Sisters Road, as a terror attack.
Witnesses described hearing the van driver shout: "I'm going to kill Muslims" and "I've done my bit".
He was restrained by members of the public at the scene, with an imam from the nearby mosque protecting him from angry members of the public.
The 47-year-old suspect has been arrested on suspicion of attempted murder and terror offences.
The man, who police believe was acting alone, was not known to the security services.
Searches are being carried out at a residential address in the Cardiff area.
The vehicle used in the attack was rented from Pontyclun Van Hire in South Wales. The firm has said it was "shocked and saddened" at the attack.
Police said all the casualties were Muslims.
The man who died had already been receiving first aid from a member of the public, police said.
Eight people have been taken to hospital, while two others were treated at the scene.
One witness Adil Rana, 24, said: "The van was driving towards us to try and basically hit us at speed.
"When he got arrested, he was taunting, saying, 'I'd do it again, I'd do it again'."
Another witness described being surrounded by bodies in the wake of the attack outside the nearby Muslim Welfare House.
Prime Minister Theresa May, who chaired a meeting of the COBRA emergency committee, condemned the attack as "every bit as sickening" as the recent atrocities in London and Manchester.
"It is a reminder that terrorism, extremism and hatred take many forms, and our determination to tackle them must be the same whoever is responsible," she said.
Later, she visited Finsbury Park Mosque and met people from a variety of faiths.
London mayor Sadiq Khan said it was a "truly horrific terrorist attack on our city".
"This attack behind me in Seven Sisters, the attack in Manchester, the attack on London Bridge, the attack on Westminster Bridge are all an attack on our shared values, our shared values of tolerance and freedom and respect," he said.
"And we will not allow these terrorists to succeed."
Metropolitan Police Commissioner Cressida Dick said it was "quite clearly an attack on Muslims".
There will be more uniformed officers at places of worship, including mosques and Muslim community centres, as police try to reassure local people.