London attacker Khalid Masood was investigated by MI5 over extremism concerns

UK police say the attacker who killed four people near Parliament in London before being shot dead yesterday was British-born Khalid Masood, who was once investigated by MI5 intelligence officers over concerns about violent extremism.

The Islamic State group claimed responsibility for the attack in a statement issued by its Amaq news agency, but did not name Masood and gave no details.

It was not clear whether the attacker was directly connected to the jihadist group.

Police said Masood, 52, was born in the county of Kent in southeast England and was most recently living in the West Midlands region of central England.

"Masood was not the subject of any current investigations and there was no prior intelligence about his intent to mount a terrorist attack," the Metropolitan Police said in a statement.

"However, he was known to police and has a range of previous convictions for assaults, including GBH [grievous bodily harm], possession of offensive weapons and public order offences."

Prime Minister Theresa May earlier told Parliament the attacker had once been investigated by the MI5 intelligence agency over concerns about violent extremism, but was a peripheral figure.

"A terrorist came to the place where people of all nationalities and cultures gather to celebrate what it means to be free, and he took out his rage indiscriminately against innocent men, women and children," Ms May said.

During five minutes of mayhem in the heart of London, Masood sped across Westminster Bridge in a car, ploughing into pedestrians.

He then ran through the gates of the nearby Parliament building and fatally stabbed an unarmed policeman before being shot dead.

Police arrested eight people at six locations in London and Birmingham in the investigation into the attack, which Ms May said was inspired by a warped Islamist ideology.

The Enterprise rental car company said the vehicle used in the attack had been rented from its Spring Hill branch in Birmingham, which is located in the West Midlands.

"An employee identified the vehicle after seeing the licence plate in an image online," company spokesman John Davies said.

"We ran another check to verify, and immediately contacted the authorities."

Death toll rises

A man injured in the attack has died in hospital, police said, bringing the total number of people killed to five, including Masood.

Police said the victim was a 75-year-old man.

About 40 people were injured in the attack, of whom 28 remain in hospital, six in critical condition.

German woman Trish Neis-Beer, who lives in South Australia and is a permanent resident of Australia, was among those hospitalised following the attack, Prime Minister Malcolm Turnbull confirmed yesterday.

Ms Neis-Beer is recovering in hospital following surgery, and has been visited by a consular representative.

"She was feeling a bit groggy, but she seems in good spirits in the circumstances," High Commissioner Alexander Downer told Channel Seven.

The dead included the stabbed policeman, Masood and three members of the public.

US tourist Kurt Cochran was named as one of the dead in a Facebook post by family member Shantell Payne.

"With a heavy heart I must pass the sad news of our beautiful brother, father, husband, son and friend Kurt Cochran, he could not overcome the injuries he received in the London terror attacks," Ms Payne wrote.

Her post said Mr Cochran's wife, Melissa Payne Cochran, was in hospital with a broken leg and rib and a cut on her head, but would recover.

Queen extends deepest sympathies to victims

The attack took place on the first anniversary of attacks that killed 32 people in Brussels, and resembled Islamic State-inspired attacks in France and Germany where vehicles were driven into crowds.

"My thoughts, prayers and deepest sympathy are with all those who have been affected by yesterday's awful violence," Queen Elizabeth said in a message.

It was the deadliest attack in Britain since 2005, when 52 people were killed by Islamist suicide bombers on London's public transport system.

Those injured in the latest attack included 12 Britons, three French children, two Romanians, four South Koreans, one German, one Pole, one Chinese, one American and two Greeks, Ms May said.