The investigation into a terrorist attack outside the Houses of Parliament in London is developing rapidly.
Here is what the Guardian has been able to confirm so far:
Five people have died, including a policeman and the attacker.
Approximately 40 other people were injured. Several are still being treated for serious injuries, including two police officers.
The assailant drove a car into pedestrians on Westminster Bridge, killing two people, before crashing it outside parliament and trying to enter the complex, armed with a knife.
He stabbed an unarmed police officer who later died from the injuries, before armed police shot him.
The police officer was identified as 48-year-old PC Keith Palmer, who had 15 years of service with the parliamentary and diplomatic protection service. He was a husband and father, police said.
Police believe the attacker struck alone and was inspired by Islamist-related international terrorism.
They think they know his identity and are investigating possible associates.
Prime minister Theresa May described the attack as "sick and depraved," but said it would not undermine British values. Parliament will sit as normal on Thursday, she said.
Three French high school students, four British university students and two Romanians were among those injured when the attacker drove into pedestrians.
One woman was thrown or jumped into the Thames from the bridge. She was rescued from the water but had sustained serious injuries.
Minister for counter-terrorism Tobias Ellwood, a former soldier, raced to give first aid to the police officer who later died. Pictures showed him with blood on his face as he administered CPR.
Scotland Yard declared the attack in Westminster, which began at about 2.40pm London time, "a terrorist incident."
London mayor Sadiq Khan vowed "Londoners will never be cowed by terrorism" in a video statement.
May was evacuated from the parliament building within minutes and driven to Downing Street.
The area was locked down and the Thames closed to all vessels between Vauxhall and Embankment as the Palace of Westminster and nearby buildings were searched by armed police.
Some MPs were confined to the Commons chamber for nearly five hours after parliamentary business was suspended.
World leaders condemned the attack and offered condolences. US president Donald Trump spoke to May, promising the UK the full support of the US government in responding to the attack.
Leaders of Canada, France, Germany and Spain were among others who sent messages of shock and solidarity.
Extra police were on duty across London, and the Metropolitan police force set up a casualty bureau for those worried about friends or family.