A European security official has told the AP news agency there was increased "chatter" on Jihadi networks Tuesday following the UK's adoption of an electronics ban aboard flights from certain mostly Muslim countries.

But he said there was no information that Westminster incident was terror-related. 

The official spoke on condition of anonymity. 

The Metropolitan Police is appealing for anyone with photos or footage of the incidents in Westminster to pass it to them. 

 "If you have photos or film of the incident in #Westminster please make sure you pass them to police "http://www.ukpoliceimageappeal.co.uk" the force tweeted.

BBC Today presenter Nick Robinson speaks to a witness on Westminster Bridge. 

Former education secretary Nicky Morgan told the Press Association: "The Division Bell had just gone and MPs were making their way to the House of Commons chamber. I was walking from Portcullis House along the path of Old Palace Yard when suddenly shots rang out. 

 "It takes a moment to realise that is actually gunfire and at that point people were yelling get down get back"

A video on Twitter appearing to show people lying injured in the road on Westminster Bridge was posted by Radoslaw Sikorski.

Mr Sikorski, a senior fellow at Harvard Centre for European Studies, told the BBC: "I heard what I thought what I thought was just a collision and then I looked through the window of the taxi and someone down, obviously in great distress.

"Then I saw a second person down, and I started filming, then I saw three more people down, one of them bleeding profusely." 

Scotland Yard said in a statement: "Police are asking people to avoid the following areas: Parliament Square; Whitehall; Westminster Bridge; Lambeth Bridge; Victoria Street up to the junction with Broadway and the Victoria Embankment up to Embankment tube. 

 "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."

House of Lords
Parliament

The House of Lords were just about to begin their regular afternoon session when the security incident occurred.

Their parliamentary annunciator system is now advising everyone in the building to "remain in their offices while armed officers conduct a sweep of the estate."

Staff and visitors at St Thomas' and Evelina London Hospitals, across the Thames from Parliament, are being advised to remain on site during the current security incident".

US President Donald Trump "has been briefed on the situation" in London and is monitoring events, his press secretary Sean Spicer tweeted.

Pauline Cranmer, of London Ambulance Service, said: "We have sent a number of resources to the scene including ambulance crews, London's Air Ambulance and our Hazardous Area Response Team. 

"As we continue to respond to the incident in #Westminster please only call for an ambulance in a genuine emergency."

Daily Mail journalist Quentin Letts whose office overlooks the scene told the BBC of the moment police shot the man.

"This man had something in his hand, it looked like a stick of some sort and he was challenged by a couple of policemen in yellow jackets and one of the yellow-jacketed policemen fell down.

"We could see the man in black moving his arm in a way that suggested he was either stabbing or striking the yellow-jacketed policeman, and one of the policemen then ran to get help, which was very quick to come and as this attacker was running towards the entrance used by MPs to get into the House of Commons.

"As he was running he ran, about I'd say 15 yard perhaps, two plain clothes guys with guns shouted at him what sounded like a warning, he ignored it and they shot two or three times and he fell."

Scotland Yard said the attack in Westminster is being treated "as a terrorist incident until we know otherwise". 

Image source, AP