UPDATE 24 March: Khalid Masood, who attacked Britain's Parliament, killing four people and wounding some 50, was born Adrian Russell Ajao, London's top counter terror officer said Friday.
Mark Rowley revealed the name in a briefing outside Scotland Yard in which he also announced two more "significant" arrests had been made. That brings the total number of people in custody for the Wednesday attack to nine.
"We remain keen to hear from anyone who knew Khalid Masood well, understands who his associates were and can provide us with information about places he has recently visited," Rowley said. "There might be people out there who did have concerns about Masood but did not feel comfortable for whatever reason in passing those concerns to us."
Masood drove his car into crowds of people on Westminster Bridge on Wednesday afternoon, killing three and wounding some 50, before stabbing a police officer to death at the Houses of Parliament. He was shot dead by police.
Rowley said two police officers targeted in the attack have significant injuries. Two other people also remain in critical condition, one with life-threatening injuries.
The latest victim, who died in the hospital on Thursday, was 75-year-old Leslie Rhodes from Streatham, south London.
UPDATE 23 March: Police have named the Westminster attacker as Khalid Masood. He was 52, born in Kent and detectives believe he was most recently living in the West Midlands, the BBC reports. Although he was known to police, there was no intelligence about Masood's intent to carry out a terrorist attack.
Earlier on Thursday, Islamic State claimed that the Westminster terrorist was a "soldier" of the terror group. After Theresa May told the Commons the killer was a British citizen who had been previously been investigated by MI5, Isil said that the attacker answered "calls to target citizens of coalition nations," The Telegraph reports.
Police have confirmed eight arrests have been made in raids following the attack and the three victims of the assailant, who also died, have been named.
Kurt Cochran was visiting London from Utah to celebrate 25 years of marriage to his wife Melissa, who was seriously hurt in the attack. Aysha Frade, a 43-year-old mother-of-two who worked at DLD College, a few hundred metres from Westminster bridge, was another victim. PC Keith Palmer, 48, died as he tried to stop the attacker in a courtyard outside the Houses of Parliament.
In her address to parliament on Thursday morning, Theresa May said "a terrorist came to the place where people of nationalities and cultures celebrate what it means to be free. This was an attack on free people everywhere."
The Queen has also issued a statement. "My thoughts, prayers, and deepest sympathy are with all those who have been affected by yesterday's awful violence," it read.
UPDATE 10.30pm: Scotland Yard's anti-terror officer Mark Rowley has confirmed that the officer who died in the Westminster attack was Keith Palmer, 48. He served in the police for 15 years. Around 40 people have been left injured following the incident.
UPDATE 6pm: Police have confirmed that four people have died in the Westminster attack, including one police officer and the attacker. Two people died on Westminster bridge. At least twenty police are said to be injured.
The French Prime Minister Bernard Cazeneuve said three French school pupils were among those harmed. "Solidarity with our British friends who have been terribly hit, full support to the injured French pupils, their families and their classmates," he wrote on Twitter.
Rex Tillerson, the US secretary of state, has also sent his condolences to the UK.
UPDATE 5:30pm: There is no indication that the terror threat level in the UK will be raised, government sources have told the BBC. It has been at 'severe' since August 2014.
UPDATE 5pm: The London ambulance service deputy director of operations, Pauline Cranmer, has confirmed that they have treated at least 10 patients on Westminster Bridge. "We have declared a major incident and our priority is to assess patients and ensure that they are treated and taken to hospital as soon as possible," she said.
The Port of London Authority has also confirmed that a seriously injured woman has been recovered from the Thames river.
In a statement, Metropolitan police commander, BJ Harrington, said a "full counter-terrorism investigation is already under way." He said there are a number of casualties but he cannot confirm how many or the nature of injuries.
"Our thoughts and his thoughts are with all those involved and responding to that incident this evening," Harrington said. "I would stress that if anyone has information about today's incident they are urged to call 0800789321 and I want to stress that if the public have any information or see anything suspicious to dial 999 immediately.
MPs and visitors to parliament have been led out through Westminster Hall. The BBC reports that Theresa May will chair a meeting of the Government's emergency Cobra committee later today.
UPDATE 4.15pm: One woman has died and a number of others have suffered "catastrophic" injuries in the incident on Westminster Bridge, a junior doctor at St Thomas' Hospital has confirmed.
Original story 3.05pm: The leader of Britain's House of Commons says a man has been shot by police at Parliament. David Lidington also said there were "reports of further violent incidents in the vicinity."
London's police said officers had been called to a firearms incident on Westminster Bridge, near the parliament. Reports suggest several people were also hit by a car on the bridge before the gunfire broke out.
An eye witness, Radoslaw Sikorski, shared a video on Twitter showing people lying injured in the road on Westminster Bridge. "A car on Westminster Bridge has just mowed down at least 5 people," he wrote.
The Metropolitan Police confirmed they were called to a firearms incident at 2.40pm on Wednesday. Less than an hour later, it was confirmed that it was being treated as "a terrorist incident until we know otherwise".
According to BBC reporter Laura Kuenssberg, three or four gunshots were heard. Political campaigner Richard Tice reported there were "ten bodies" seen on Westminster Bridge.
Alan Parry, a Sky Sports presenter who was at the scene, said he heard an "almighty crash" and saw a 4x4 crashed into the railings outside Parliament.
"The guy who was the driver of the 4x4 got out of the car and sprinted away from the scene. That was followed by four what sounded like gun shots and all hell was let loose, police descended everywhere," he said.
Prime Minister Theresa May was seen getting into a silver Jaguar car during the incident. Staff inside Parliament were told to stay inside their offices.
David Lidington told MPs: "Colleagues will have appreciated that events have been moving rapidly and I want to emphasise that the knowledge that I have which is definite is so far very limited.
"What I am able to say to the House is that there has been a serious incident within the estate. It seems that a police officer has been stabbed; that the alleged assailant was shot by armed police.
An air ambulance is attending the scene to remove the casualties. There are also reports of further violent incidents in the vicinity."
In a statement, the police said: "This is to allow the emergency services to deal with the ongoing incident. Officers - including firearms officers - remain on the scene and we are treating this as a terrorist incident until we know otherwise.We thank the public for their assistance."