Westminster attack: The victims
Westminster Bridge - where the attacker drove into pedestrians before stabbing a police officer - is situated in a busy tourist spot in London with its views of parliament's Big Ben clock tower, and the injured included many foreigners.
Here is what we know about the victims so far.
'Hero' police officer
Unarmed police officer Keith Palmer, who was fatally stabbed as he stood guard at an entrance to parliament, has been hailed as a hero.
The 48-year-old husband and father had been a police officer for 15 years and was part of the parliamentary protection force.
Prime Minister Theresa May called him "every inch a hero".
He previously served in the British army alongside James Cleverly, now a Conservative MP, who tweeted: "A lovely man, a friend. I'm heartbroken."
Cleverly paid an emotional tribute to Palmer in the House of Commons and asked that he receive a posthumous award for his actions.
As a tribute, Charlton Athletic football club placed a scarf in its red and white colours on Seat 166 of its stadium, which Palmer held as a season ticket holder.
Colleagues of Aysha Frade, a mother who was run down and killed as she headed to pick up her children, said she was "loved" and would be "deeply missed".
A Spanish diplomatic source confirmed to AFP that Frade was a 43-year-old British national whose mother was Spanish.
|Aysha Frade was killed as she headed to pick up her children
Media reports said her daughters were seven and nine-years-old.
Rachel Borland, principal of DLD College London where Frade worked in the administration team, said she was "highly regarded and loved by our students and by her colleagues".
"She will be deeply missed by us," she added.
Man from Utah
Kurt Cochran from Utah in the US has been named as the third victim.
The news was announced on Facebook by a Shantell Payne, an apparent relative of the victim's wife Melissa Payne Cochran.
Cochran "could not overcome the injuries he received in the London terror attacks", Payne wrote in her post.
|The pain is so heart-wrenching and raw it has rocked our family and all that knew him to its core
"The pain is so heart-wrenching and raw it has rocked our family and all that knew him to its core."
She said Cochran's wife was also in hospital where she is recovering from a broken leg and rib and a cut on her head.
The BBC quoted Cochran's father-in-law Clint Payne as saying: "Our family is heartbroken."
The police said only that a man in his 50s had died.
Police said 29 of around 40 people wounded were treated in hospital. Seven remained in a "critical condition" on Thursday.
Three French pupils on a school trip to London, all of them aged 15 or 16, were among those hurt, including two who suffered broken bones but were not reported to be in life-threatening condition.
The teenagers are from a high-school in Concarneau, in the western Brittany region, and were joined by their families on Wednesday evening. French Foreign Minister Jean-Marc Ayrault arrived in London on Thursday to visit them.
|Five South Korean tourists in their 50s and 60s were wounded after being knocked to the ground by people fleeing as the assailant mowed down pedestrians
Five South Korean tourists - four women and a man in their 50s and 60s - were also wounded after being knocked to the ground by people fleeing as the assailant mowed down pedestrians, Seoul's foreign ministry said.
In an address to parliament on Thursday, Prime Minister Theresa May said that among the people admitted to hospital were 12 Britons as well as one German, one Pole, one Irish citizen, one Chinese national, one Italian, one American, two Greeks and two Romanians.
A woman with serious injuries rescued from the River Thames near Westminster Bridge after the attack, as well as her fiance, are believed to be the two Romanians.
Local media in the Eastern European country have named them as Andreea Cristea, a 29-year-old architect and Andrei Burnez. Authorities did not confirm the reports.
The injured also included three police officers who were returning from an event recognising their bravery, two of whom remain in serious condition.
Among the injured British nationals were four students from Edge Hill University in Ormskirk in North West England who were on an educational visit to the parliament. Two of them were described as "walking wounded".