Four dead, including a police officer, after terrorist attack in Westminster, London. Lone suspect shot dead by police after fatally stabbing PC Keith Palmer inside the grounds of the Houses of Parliament. Two victims identified: Brit Aysha Frade and US tourist Kurt Cohran. A car drove into pedestrians on nearby Westminster Bridge. At least 40 are being treated for injuries, some “catastrophic.” ISIS claims responsibility for the attack. WARNING: Some of the images below are graphic. Our live coverage of the investigation into the attack continues here. News about the identities of the victims can be found here.

LONDON – Four people, including a police officer, have died and at least 40 were injured in what is being treated as a terror attack in Westminster, London, on Wednesday afternoon.

A lone assailant mowed down dozens of pedestrians on Westminster Bridge in a 4X4 car, before killing a police officer with a knife in the grounds of Parliament just after 2.30 p.m. GMT yesterday.

The police officer was named by the Metropolitan Police at around 22:30 p.m GMT on Wednesday night as PC Keith Palmer, 48, a husband and father with 15 years’ service. The suspect, who is yet to be named, was shot dead by police. The attacker was described by witnesses as Asian and in his forties.

Midday on Thursday, ISIS (also known as the Islamic State and Daesh), claimed responsibility for the attack via a jihadist news site Amaq:

A Met Police statement released late on Wednesday night put the death toll at five but that number has been revised, with four people now understood to have been killed. Two other police officers were treated for injuries.

Two of the members of the public to be killed in the attacks has been named.

The first is Aysha Frade, a 43-year-old British woman of Galician origin and mother of two, according to Spanish newspaper La Voz de Galicia. The second is Kurt Cohran, a tourist from Utah, Metro is reporting.

The report adds that Frade was leaving the DLD sixth form college near in Westminster where she taught Spanish when she was hit by the terrorist's car on Westminster Bridge.

Police have raided six addresses and arrested eight people since the attacks.

Speaking on Thursday morning, Assistant Commissioner for Specialist Operations Mark Rowley said: "We need the public's help. The police are the public and the public are the police. I would urge anyone in this great city, if they are concerned or worried, about anything to approach a police officer and talk to them."

He added: "Police officers will be talking to Londoners. That is part of what we do. We are leading a large response that covers all of London and national government in relation to the response of this incident. We are working with all the emergency services and local agencies in London to ensure the response is of a high quality, high calibre, and it is about keeping Londoners safe."

The Acting Commissioner said on Wednesday that the Met believes it knows the identity of the terrorist but would not disclose any further details other than he was thought to be inspired by Islamist-related international terrorism.

He advised the public to be vigilant and confirmed additional officers will patrol the capital tonight and Thursday.

Westminster Bridge has now re-opened but investigations continue in the area. Here is a picture taken outside St Thomas' Hospital, by Westminster Bridge, this morning where some of the injured were treated yesterday.

St Thomas' Hospital Westminster

Foto: source Lianna Brinded/Business Insider

Scotland Yard has confirmed that a major terrorist investigation is underway involving hundreds of officers. They are looking at the history, associates, and background of the attacker.

A minute's silence was held in parliament and at Scotland Yard at 9:33 a.m on Thursday morning while London Mayor Sadiq Khan has announced a vigil will take place in Trafalgar Square at 6 p.m (GMT) on Thursday evening.

Speaking early on Wednesday, Prime Minister Theresa May described the attacks as "sick and depraved" and thanked the "exceptional men and women" who put their lives on the line to protect London.

You can read May's full reaction here.

Reports have suggested that the below Press Association photo is the first image of the suspect. The alleged intruder was treated by medics and loaded into an ambulance.

Westminster terror

Foto: sourcePA

The man seemed to be carrying a "long kitchen knife" prior to being shot, Press Association political editor Andrew Woodcock told the BBC. The car he was drove was a Hyundai 4x4 rented from an Enterprise branch in Solihull.

Conservative MP Tobias Ellwood attempted to give mouth-to-mouth to the stabbed police officer before he died. Acting Commissioner Craig Mackey was at the scene and is being treated as a significant witness.

A source who has spoken to MPs in Parliament at the time of the attack told Business Insider: "MPs walking through [the] yard were told armed shooter and told to dive and run for cover - many ended up in tube tunnel. While people were shouting 'run' Ellwood strode the other way to help victims."

Three of the injured were French students, five were from South Korea, and two from Romania. A woman who jumped into the River Thames during the incident was pulled out alive soon after the attack.

Westminster

Foto: source Stefan Wermuth / Reuters

Journalist Quentin Letts gave an account of what he saw at Parliament to MSNBC.

"I saw a fairly thick-set man wearing black clothes running through the open gates, the security gates where people drive their cars," Letts said. "He seemed to have something in his hand, maybe a knife, maybe a stick."

Letts continued: "He started beating a policeman who had fallen over on the ground. The policeman managed to shake him off and the attacker then ran towards the entrance of the House of Commons, which is used by our members of Parliament and he got about 15 yards before the authorities responded."

A witness close to Westminster Bridge told Business Insider that there were "lots of sirens" and "people running" at the scene of the Westminster Bridge incident.

A man gives his account of what happened on Westminster Bridge:

WATCH: Eyewitness says he sawa car crash into pedestrians at scene of #Westminsterattack. More updates here: https://t.co/tQ6G5eN6xu pic.twitter.com/8E69CHg8PM

#Westminsterhttps://t.co/tQ6G5eN6xupic.twitter.com/8E69CHg8PMMarch 22,2017

All government and civil servants were kept inside Westminster Hall hours after the incident but began to make their way out of the building shortly after 8 p.m. local time on Wednesday night.

Westminster tube station and nearby buildings including St Thomas' Hospital and the Gherkin building were also on lockdown until early evening. Armed officers are still patrolling the area.

Westminster

Foto: An air ambulance helicopter lands to tend to the wounded. source Stefan Wermuth / Reuters

Facebook activated the safety check feature to allow those in London to let people know they're safe while Londoners made #WeAreNotAfraid a global trend on Twitter in a display of defiance and solidarity.

Here is footage of people fleeing the scene outside parliament:

4 people have died in anattack in London. This video shows the moment the incident beganoutside the UK Parliament.https://t.co/FwKsndgisW pic.twitter.com/81srJq9yGr

https://t.co/FwKsndgisWpic.twitter.com/81srJq9yGrMarch 22,2017

No terrorist group has so far accepted responsibility for the attack. New York Times terrorism correspondent Rukmini Callimachi noted on Twitter, however, that pro-ISIS channels on the chat app Telegram are talking about the attack.

"Numerous ISIS-linked channels are sharing blow-by-blow updates on events in London," Callimachi said, noting that this pattern follows that of other recent terror attacks.

"We saw this post-Paris, post-Nice, post-Orlando etc," she said. "The mode of attack, according to reporters at the scene, includes stabbing and car-ramming, both ISIS signatures."

Wednesday marks the first anniversary of the worst terrorist attack in Belgium's history, in which 32 people were killed and hundreds were wounded in a bombing at the airport in Brussels. Callimachi, the Times terrorism reporter, noted that "ISIS, like al-Qaeda, loves anniversaries."

Westminster

Foto: source Toby Melville / Reuters

A woman assists an injured person after an incident on Westminster Bridge in London, March 22, 2017. REUTERS/

Foto: A woman assists an injured person after an incident on Westminster Bridge in London, March 22, 2017. source Reuters / Toby Melville

Prime Minister Theresa May was in Parliament at the time of the attack but is safe, a spokesperson confirmed. She was ushered into a car and driven away from the scene.

Conservative Nigel Evans MP told Sky that another MP ran into the chamber as a vote was taking place exclaiming "has anyone seen the Prime Minister?" while the attack was unfolding outside.

Scottish Parliament suspended the second day of a debate on an independence referendum motion. US President Donald Trump was briefed on the situation, his spokesperson Sean Spicer confirmed.

London Mayor Sadiq Khan thanked London emergency services for their "tremendous bravery in exceptionally difficult circumstances" and later released a video statement saying "Londoners will never be cowed by terrorism."

In a statement, Khan said: "There has been a serious incident near to Parliament Square this afternoon which is being treated as a terrorist attack until the police know otherwise.sadiqkhan2

Foto: sourceSky News

"I have spoken to the Acting Commissioner.

"The Metropolitan Police Service is dealing with the incident and an urgent investigation is underway. My thoughts are with those affected and their families.

"I would like to express my thanks to the police and emergency services who work so hard to keep us safe and show tremendous bravery in exceptionally difficult circumstances.

"For the latest information please visit news.met.police.uk."

The Archbishop of Canterbury also posted a message via Twitter:

US President Donald Trump released the details of his calls with May around 8 p.m. GMT:

Some victims were hit near the London Eye end of the bridge (below) while others were injured nearer Parliament:

Westminster

Foto: source Toby Melville / Reuters

Pedestrians make their way across Westminster Bridge after the attack:

Westminster

Foto: source Toby Melville / Reuters

Bystanders try to help the wounded:

Westminster

Foto: source Toby Melville / Reuters

Armed police were on the scene in minutes to escort people out of the area:

An armed police officer assists a woman after an incident on Westminster Bridge in London, March 22, 2017.

Foto: source REUTERS/Toby Melville

Westminster Bridge is incredibly crowded at all times. It is heavily used by tourists, Westminster workers and other commuters:

A man lies injured after a shottingt incident on Westminster Bridge in London, March 22, 2017.

Foto: source REUTERS/Toby Melville

The vehicle appears to have struck several people along the length of the bridge as it headed toward Parliament:

A woman lies injured after a shottingt incident on Westminster Bridge in London, March 22, 2017. REUTERS/Toby Melville

Foto: source Reuters / Toby Melville

The area around Big Ben, the House of Commons, and the London Eye was brought to a standstill:

westminsterbridge2

Foto: source Business Insider/Donald Sinclair

Debris littered the bridge:

Westminster

Foto: source Toby Melville / Reuters

Here was the scene at Parliament after a car drove into the gate:

https://twitter.com/AlexSmith1964/status/844565336875782145

Here was the scene on Westminster Bridge earlier today:

http://instagr.am/p/BR8fAH_D91o

This witness saw five people hit by the car:

MPs inside the Houses of Parliament

This is the moment Parliamentwas suspended as "sounds similar to gunfire" were heardoutside pic.twitter.com/to6PPxkNqL

pic.twitter.com/to6PPxkNqLMarch 22,2017

Police are appealing for images and videos of the Westminster attacks. Help the police force and upload here.

The police have also provided a hotline for those worried about friends or family that may be involved in the incidents:

This is a developing story...