The Westminster attacker was British-born and known to the police and intelligence services, the prime minister has revealed. In a statement to the Commons, Theresa May said he had been investigated some years ago over violent extremism but had been a peripheral figure by WEST Mail News.
"He was not part of the current intelligence picture," she said.
Eight arrests have been made following the attack on Wednesday that left four dead.
Those that died are PC Keith Palmer, Aysha Frade who worked at a London college, a man in his 50s and the attacker.
Seven of the injured are still in hospital in a critical condition.
A further 29 had been treated in hospital, Mr Rowley added.
In the attack on Wednesday afternoon, a man drove a car along a pavement on Westminster Bridge knocking down pedestrians, creating panic and leaving dozens injured.
He then ran towards Parliament where he stabbed PC Palmer who was unarmed. Armed police then shot dead the attacker in the grounds.
Mrs May paid tribute to PC Palmer saying: "He was every inch a hero and his actions will never be forgotten."
Mrs Frade worked at a London sixth form college just a few hundred metres from Westminster Bridge.
Principal at DLD College, Rachel Borland, said she was "highly regarded and loved by our students and by her colleagues".
Keith Palmer stopped the attacker in his tracks. Aysha Frade would be deeply missed by all, the principal at the college said
- Live coverage
- Armed raid on Birmingham flat
- What we know so far
- May condemns attack
- Eyewitness accounts
- In pictures: The scene in Westminster
In an earlier statement made outside Scotland Yard, Acting Deputy Commissioner Mark Rowley said seven arrests had been made during raids in London and Birmingham - an eighth was announced several hours later.
"It is still our belief - which continues to be borne out by our investigation - that this attacker acted alone and was inspired by international terrorism.
"To be explicit, at this stage we have no specific information about further threats to the public."
He urged journalists not to publish the attacker's name while searches were continuing.
He said Londoners should expect to see more police officers on the streets, after officers' leave had been cancelled and duty hours extended.
It was initially thought that three members of the public had been killed on Westminster Bridge, but Mr Rowley referred to just two in his statement.
Director General of MI5 Andrew Parker condemned the attack as "appalling and disgusting".
The agency's operational response was "fully mobilised in support of the police", he said.
Media captionMet Police Acting Deputy Commissioner Mark Rowley gave update on the investigation early this morning
In other developments:
- A witness told the Press Association that three men were arrested in an armed raid on a Birmingham address. The BBC understands this is linked to the London attack
- There is an unconfirmed suggestion that the car used in the attack was hired from an address in Birmingham, BBC Newsnight says
- Security at Parliament will be reviewed, says Defence Secretary Sir Michael Fallon
- The flag over the Houses of Parliament is flying at half mast
- MPs held a minute's silence before Parliament continued business as normal
- People worried about family and friends can call the police casualty bureau on: 0800 056 0944 or 0207 158 0010. Anyone with images or footage of the incident can send them to ukpoliceimageappeal.co.uk
Image copyright HoC
Defence Secretary Sir Michael Fallon told BBC Radio 4's Today programme the "working assumption" was that the attack was linked to "Islamic terrorism in some form".
He paid tribute to Pc Palmer, a 48-year-old father and husband, and an unarmed member of the Parliamentary and Diplomatic Protection Squad who had served for 15 years.
Pc Palmer stopped the attacker getting into Parliament and "gave his life for the democracy we all cherish", he told BBC Breakfast.
Asked about the mood of the city, Sir Michael said: "London is getting back to normal. They've seen terrorism like this before and they are not going to let it triumph."
Image copyright FOTOX.TOP
Brendan Cox, the husband of murdered MP Jo Cox, said it was important to remember that "this was a story about people who didn't come home yesterday".
US President Donald Trump was among world leaders to offer their support to Mrs May, tweeting: "Spoke to UK Prime Minister Theresa May today to offer condolences on the terrorist attack in London. She is strong and doing very well."
The Pope said in a letter to the Archbishop of Westminster that he had been "deeply saddened to learn of the loss of life and the injuries" and "assured the nation of his prayers".
By Dominic Casciani, home affairs correspondent
The carnage on Westminster Bridge and inside the grounds of Parliament is the attack that security chiefs here in the UK have long been preparing for.
Terrorism looks not just to kill and maim - but to create panic and such a sense of disorder that it rocks a city or nation to its foundations.
And this attacker sought to do so in as low-tech way as is possible.
The days when terrorism meant large, complex bombs and months of planning are gone: Western security agencies - particularly MI5 and its partner agencies - are very, very good at identifying those plots and disrupting them.
The longer it takes to plan such an attack, the more people who are involved, the more chances there will be for security services to learn what is going on.