It was the deadliest attack in London since four British Islamists killed 52 commuters and themselves in suicide bombings on the transport system in July 2005, London's worst peacetime attack.
British police have arrested seven people in the investigation into an attacker who killed four people and injured about 40 before being shot to death by police, Britain's most senior counter-terrorism officer said on Thursday.
Mark Rowley said the latest figures were that there were four dead including the attacker and 29 people being treated in hospital, seven of whom were in a critical condition. Police had said late on Wednesday that the death toll was five.
Rowley said police had searched addresses in London, Birmingham and other parts of the country in their investigation.
"It is still our belief ... that this attacker acted alone and was inspired by international terrorism. At this stage we have no specific information about further threats to the public," Rowley said.
He said there was a mix of nationalities among the dead but gave no details. The victims were a policeman who was stabbed and two members of the public, a woman in her mid-40s and a man in his mid-50s.
The fourth dead was the assailant. Police believe they know the identity of the attacker but have not named him.
The attack on Wednesday started when the assailant sped across Westminster Bridge in a car, ramming pedestrians along the way. He then ran towards parliament and stabbed the policeman before he was shot.
Three French high-school students aged 15 or 16, who were on a school trip to London with fellow students from Brittany, were among the injured.
Five South Koreans were also wounded near the British parliament on Wednesday in what police called a "marauding terrorist attack", South Korea's foreign ministry said in Seoul.
1. Westminster Bridge
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A woman assists an injured person after an incident on Westminster Bridge in London, Britain March 22
Image courtesy: Reuters
2. Crash Site
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People stand near a crashed car and an injured person lying on the ground, right, on Bridge Street near the Houses of Parliament in London, Wednesday, March 22, 2017. Britain has been targeted Wednesday by what authorities are calling a terrorist incident, after vehicle mowed down pedestrians on London's Westminster Bridge, killing at least one woman and leaving others injured, around the same time as a knife-wielding attacker stabbed a police officer and was shot on the grounds outside the British Parliament.
(Image obtained from James West's Twitter by AFP)
3. Central London
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Paramedics load a victim into the back of an ambulance as members of the emergency services work on Westminster Bridge, alongside the Houses of Parliament in central London on March 22, 2017, during an emergency incident.
Image courtesy: AFP
4. Westminster Bridge
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An injured woman is assisted after an incident on Westminster Bridge in London, Britain March 22, 2017
Image courtesy: Reuters
5. London Eye
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British Police officers stand between the pods of the London Eye, during the evacuation of passengers, in central London on March 22, 2017, in the aftermath of a terror incident at the Houses of Parliament. Police guarding the iconic House of Commons building shot the man but several people were left with "catastrophic" injuries on Westminster Bridge, a busy traffic junction popular with tourists with views of Big Ben.
Image courtesy: AFP
6. British Police Forensic Officers
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British police forensics officers work near a grey vehicle that crashed into the railings of the Houses of Parliament in Westminster, central London on March 22, 2017, in the aftermath of a terror incident.
Image courtesy: AFP
7. Westminster Bridge
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An injured man sits covered with a blanket as emergency services staff provide medical attention to injured people on the south side of Westminster Bridge, close to the Houses of Parliament in London, Wednesday, March 22, 2017. London police say they are treating a gun and knife incident at Britain's Parliament "as a terrorist incident until we know otherwise."
Image courtesy: PTI
8. Forensic Investigators
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Forensics investigators work at the scene after an attack on Westminster Bridge in London, Britain March 22, 2017.
Image courtesy: Reuters
9. Emergency Services
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Emergency services respond after an incident on Westminster Bridge in London, Britain March 22, 2017.
Image courtesy: Reuters
10. Tobias Ellwood
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Conservative Member of Parliament Tobias Ellwood, centre, helps emergency services attend to an injured person outside the Houses of Parliament, London, Wednesday, March 22, 2017.
Image courtesy: PTI
