Five people have died and 40 injured after a car and knife attack in London on Wednesday.
Here's what we know, so far, about the terror attack - and how the world has reacted:
Five people - a police officer, three members of the public and the attacker - died.
The officer has been named as Pc Keith Palmer, a 48-year-old husband and father with 15 years of police service.
Aysha Frade and American tourist Kurt Cochran died in the attack on Westminster Bridge
On Thursday night, police said a 75-year-old man had died in hospital following the attack
Another woman ended up in the Thames. It is unknown whether she fell or was hit by the vehicle. She was pulled from the water and treated for serious injuries.
A group of French schoolchildren from the western Britanny region were caught up in the attack. Three were injured.
On Wednesday evening, French President Francois Hollande said a plane is set to fly to London to bring the families of the students to their loved ones.
Romania's foreign ministry said two Romanians were wounded in the deadly attack.
Two police officers were also hit by the vehicle and remain in a "serious" condition in hospital.
After speeding down Westminster Bridge, the attacker crashed his car into the railings encircling the Palace of Westminster. He left the car with two knives and stabbed Pc Keith Palmer as he entered the grounds.
The suspect - who has been identified as Khalid Masood - was shot dead moments later by another officer.
The police response
Police are treating the incident as a terrorist attack, with Scotland Yard's top anti-terror officer Mark Rowley saying the attacker was "inspired by international terrorism".
Eight people have been arrested at addresses raided in London, Birmingham and elsewhere in connection with the Westminster terror attack, police said.
Craig Mackey, the Acting Commissioner of Scotland Yard, happened to be at the scene of the terror attack and is providing evidence as a key witness.
The Government reaction
Prime Minister Theresa May chaired a meeting of the Government's COBRA committee on Wednesday evening and later described the attack as "sick and depraved".
She said Parliament will resume on Thursday morning and urged Londoners to "get up and go about their day as normal".
Defence Secretary Michael Fallon has said the working assumption is that the Westminster attack is linked to Islamic terrorism.
World pays tribute to terror victims
Communities around the world have shown solidarity with those affected by Wednesday's attack through a series of poignant gestures.
As midnight fell in Paris, the Eiffel Tower switched its famous lights off to honour those who died.
Ron Huldai, the mayor of Tel Aviv, posted an image of the City Hall building, illuminated in the colours of the Union flag.
Israeli Deputy Foreign Minister Tzipi Hotovely expressed his country's "deep shock" and offered solidarity with the victims.
US President Donald Trump was among several world leaders quick to offer their support.
In a tweet posted overnight, he confirmed that he spoke to Theresa May and offered his "condolences on the terrorist attack in London".
Meanwhile German Chancellor Angela Merkel said her thoughts were "with our British friends and all of the people of London" with the European Commission President Jean-Claude Juncker saying his thoughts "were with London tonight".
Canadian Prime Minister Justin Trudeau added he was "shocked and saddened to learn of the innocent people who were killed and injured as a result of this cowardly attack."
He added that Canadians "stand ready to offer all possible assistance to the British government" and the UK "will emerge from their grief stronger and more united than ever before".
First Minister for Scotland, Nicola Sturgeon, said her thoughts are with "everyone... caught up in this dreadful incident".
French President Francois Hollande offered his condolences to those who died in the attack and expressed France's solidarity with Britain "in this tragic ordeal."
Spanish Prime Minister Mariano Rajoy condemned the deadly rampage and said "we must remain united."