Three people were injured on Tuesday after British police say a man deliberately drove a car into pedestrians and cyclists before ramming it into barriers outside London's parliament.
The driver, a man in his 20s, was arrested by armed officers at the scene moments later in an incident that police are calling the second terrorism attack on the building in just under 18 months.
"Given that this appears to be a deliberate act, the method, and this being an iconic site, we are treating it as a terrorist incident," London Assistant Commissioner Neil Basu said.
In March 2017, Khalid Masood, 52, killed four people on nearby Westminster Bridge and stabbed to death an unarmed police officer in the grounds of parliament before being shot dead.
It was the first of five attacks on Britain last year which police blamed on terrorism, three of which involved vehicles being used as a weapon.
Basu said the suspect in Tuesday's incident was in custody but was not co-operating with detectives. Although he had not been formally identified, the man was not believed to be known to security forces, Basu added.
"At this early stage of the investigation, no other suspects at the scene have been identified or reported to police," Basu said. "There is no intelligence of further danger to Londoners or the rest of the UK in connection with this incident."
Police said a silver Ford Fiesta had collided with a number of cyclists and pedestrians before crashing into barriers outside the Houses of Parliament in the early hours of Tuesday morning. No other weapons had been found, Basu said.
Camera footage showed the vehicle taking a wrong turn into a group of cyclists waiting at traffic lights before veering across the road and into a lane leading to parliament before hitting the barrier as two police officers jumped to safety.
Two people were taken to hospital and one woman was still receiving treatment for serious but not life-threatening injuries.
Armed officers swarmed the scene and cordoned off a large area around the parliament building in central London, usually bustling with tourists and government workers.
'It looked planned'
"I saw the cyclists, injured cyclists. I don't know if he's hit these people, or if they've just dived to escape," witness Jason Williams told reporters. "It didn't swerve, there was not another car going behind him. It looked like it was planned."
Images shot by a Euronews journalist showed police pointing their guns at the vehicle shortly after the crash. Footage on social media showed a handcuffed man being led away by heavily armed police.
British Prime Minister Theresa May, who like other lawmakers is on holiday during parliament's summer recess, said her thoughts were with the people injured. Government security officials were due to hold a meeting of their emergency committee today to discuss the incident.
"All Londoners, like me, utterly condemn all acts of terrorism on our city," London's Mayor Sadiq Khan said on Twitter.
US President Donald Trump, who has previously spoken out about security issues in London, also commented on the incident.
"These animals are crazy and must be dealt with through toughness and strength," Trump said on Twitter.
Westminster Underground station, close to parliament, was closed to the public and the building cordoned off.
Nigel Evans, a lawmaker from May's Conservative Party, said the incident had shown security measures at parliament were effective but might still need to be reviewed.
"I’m sure that (debate about) pedestrianization of Parliament Square and which vehicles should be able to access so closely in parliament will be reignited," he told BBC TV.
Britain is on its second-highest threat level of "severe," meaning an attack is considered highly likely and the authorities say a dozen Islamist plots had been foiled since Masood's attack in Westminster last year.
Last week, a Muslim convert admitted plotting to kill more than 100 people by driving a truck into pedestrians on London's Oxford Street, the capital's major shopping thoroughfare.
In October last year, 11 people were injured when a car collided with pedestrians near London’s Natural History Museum, raising fears of an attack, but police later said the incident was a road traffic accident.
By Kylie MacLellan and Hannah McKay/Reuters
Additional reporting by Michael Holden, James Davey, Alistair Smout and Paul SandleWriting by William Schomberg; Editing by Janet Lawrence, William Maclean.