LONDON (March 23): The attacker who killed three people near parliament before being shot dead was British-born and was once investigated by MI5 intelligence officers over concerns about violent extremism, Prime Minister Theresa May said on Thursday.

Islamic State claimed responsibility for the attack in a statement issued by its Amaq news agency, but it gave no name or details and it was not clear whether the attacker was directly connected to the jihadist group.

Police arrested eight people at six locations in London and Birmingham in the investigation into Wednesday's lone-wolf attack that May said was inspired by a warped Islamist ideology.

About 40 people were injured of whom 29 remain in hospital, seven in critical condition, after the incident which resembled Islamic State-inspired attacks in France and Germany where vehicles were driven into crowds.

The assailant sped across Westminster Bridge in a car, ploughing into pedestrians, then ran through the gates of the nearby parliament building and fatally stabbed an unarmed policeman before being shot dead.

"What I can confirm is that the man was British-born and that some years ago he was once investigated by MI5 in relation to concerns about violent extremism," May said in a statement to parliament.

"He was a peripheral figure ... He was not part of the current intelligence picture. There was no prior intelligence of his intent or of the plot," she said, adding his identity would be revealed when the investigation allowed.

The mayhem in London came on the first anniversary of attacks that killed 32 people in Brussels.

The dead were two members of the public, the stabbed policeman and the attacker.

"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.

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," Payne wrote.

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

"TOOK OUT HIS RAGE"

Westminster Bridge and an area around parliament were still cordoned off early on Thursday and forensic investigators in light blue overalls examined the scene where the attacker was shot. The bridge re-opened on Thursday afternoon.

It was the deadliest attack in Britain since 2005, when 52 people were killed by Islamist suicide bombers on London's public transport system. Police had given the death toll as five but revised it to four on Thursday.

The casualties included 12 Britons, three French children, two Romanians, four South Koreans, one German, one Pole, one Chinese, one American and two Greeks, May said.

"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," said May.

A minute's silence was held in parliament and in front of police headquarters at 0933 GMT, in honour of the victims — 933 was the shoulder number on the uniform of Keith Palmer, the policeman who was stabbed to death.

May was in parliament at the time of the attack, a short distance away from the spot where the attacker was shot. She was whisked away as the chaos erupted.

A government minister was widely praised for trying to resuscitate Palmer, walking away from the scene with blood on his hands and face.

A crowdfunding page hastily set up to raise money for Palmer's family attracted close to 78,000 pounds ($97,600) within five hours.

Many have been shocked that the attacker was able to cause such mayhem in the heart of the capital equipped with nothing more than a hired car and a knife.

"This kind of attack, this lone-wolf attack, using things from daily life, a vehicle, a knife, are much more difficult to forestall," Defence Minister Michael Fallon told the BBC.

"ACTS OF NORMALITY"

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.

French Foreign Minister Jean-Marc Ayrault travelled to London to show solidarity and met some of the other students who were on the school trip and their families at a hotel near the hospital where the injured were being treated.

He told reporters the lives of the three youngsters were not in danger. Ayrault later attended the session in parliament where May spoke. France has been hit by repeated deadly Islamist attacks over the past two years.

A vigil was planned in London's Trafalgar Square at 6pm (1800 GMT)

May said the fact that normal life was going on across Britain was the greatest response to the attack.

"It is in these actions – millions of acts of normality — that we find the best response to terrorism, a response that denies our enemies their victory," she said.

Britain's plan to trigger the formal process of exiting the European Union on March 29 will not be delayed, May's spokesman said.

Faith leaders from the Muslim, Hindu, Christian and Sikh communities met with officers from London's Metropolitan Police on Thursday, police said, as authorities vowed to prevent any surge in hate crime in the wake of the attack.

Anti-immigration groups were quick to make links between immigration and the attack, though it was subsequently revealed the attacker was British-born.

Leave.EU, a group that has campaigned for immigration to be severely restrained as part of Britain's EU exit, accused mainstream politicians of facilitating acts of terror by failing to secure borders.

In France, far-right presidential candidate Marine Le Pen also drew a link, saying events in London highlighted the importance of protecting national borders and stepping up security measures.