Prime Minister Theresa May condemned what she called a sickening terrorist attack on Muslim worshippers in London on Monday.
A van ploughed into worshippers near a mosque in the early hours of Monday, injuring 10 people, two of them seriously.
The vehicle swerved into a group of mainly North and West African people shortly after midnight as they left prayers at the Muslim Welfare House and the nearby Finsbury Park Mosque in north London, one of the biggest in Britain.
The driver, identified by British media as 47-year-old Darren Osborne, was grabbed at the scene by locals and pinned down until police arrived.
The attacker was not named by police but local media reported he was a father of four who lived in Wales.
He was held on suspicion of attempted murder which was later extended to preparing or instigating terrorism, including murder and attempted murder.
After being seized, he said he had wanted to kill "many Muslim people", one witness told journalists.
A man, who had earlier suffered a heart attack, died at the scene but it was not clear if his death was connected to the van attack.
"This morning, our country woke to news of another terrorist attack on the streets of our capital city: the second this month and every bit as sickening as those which have come before," May told reporters outside her Downing Street office.
"This was an attack on Muslims near their place of worship," said May who later visited the mosque.
TRT World's Sara Firth reports from London.
US ready to provide support
The White House said US President Donald Trump was receiving regular updates on the attack.
"We've made it very clear to our British allies that we stand ready to provide any support and assistance that they may need," White House spokesman Sean Spicer told reporters at a briefing.
The attack was the fourth since March in Britain and the third to involve a vehicle deliberately driven at pedestrians.
It came at a tumultuous time for the government with Britain starting complex divorce talks with the EU and May negotiating with a small Northern Irish party to stay in power after losing her parliamentary majority in a snap election.
The mosque's worshippers had just left special prayers during the Muslim holy month of Ramadan.
Usain Ali, 28, said he heard a bang and ran for his life.
"When I looked back, I thought it was a car accident, but people were shouting, screaming and I realised this was a man choosing to terrorise people who are praying," he told Reuters. "He chose exactly the time that people pray, and the mosque is too small and full, so some pray outside."
Another witness Yann Bouhllissa, 38, said he had been tending an old man who had suffered a heart attack when the van was driven at them. The driver was then seized by locals.
"One guy caught the guy and brought him down," Bouhllissa said. "When he was on the floor, the guy asked 'why do you do that?'. He said 'Because I want to kill many Muslim people'."
Mohammed Mahmoud, the imam from the Muslim Welfare House, stepped in to ensure the van driver was not hurt until he was bundled into a police van.
Neil Basu, senior national coordinator for counter-terrorism policing, said restraint shown by locals was "commendable."
Security Minister Ben Wallace said the man was "not known to the authorities in the space of extremism or far-right extremism."
Police, who believe he was acting alone, were searching addresses in Cardiff, Wales, where the vehicle hire company that the van was rented from is based.
The latest incident took place just over two weeks after three militants drove into pedestrians on London Bridge and stabbed people at nearby restaurants and bars, killing eight.
A suicide bombing at a pop concert in Manchester, northern England, in May also killed 22 people, while in March, a man drove a rented car into pedestrians on Westminster Bridge in London and stabbed a policeman to death before being shot dead. Five people were killed in that attack.