Donald Trump has said the “terrorist attack” in Westminster on Tuesday morning was conducted by “animals”.
Counter-terror police are investigating after a car crashed into security barriers outside the Houses of Parliament, injuring two people.
A driver has been arrested on suspicion of terror offences after a car collided with cyclists and pedestrians before crashing.
The man, in his late 20s, is being held in custody at a south London police station after armed officers swarmed the scene just before 7.40am.
Scotland Yard has said the man is not known to police or MI5.
Two people were taken to hospital, while a third person with minor injuries was assessed at the scene, the London Ambulance Service (LAS) said.
Theresa May said her thoughts were with those injured and thanked the emergency services for their “immediate and courageous” response.
Jeremy Corbyn said the incident was “appalling” and “shocking”.
“I think we say a big thank you to the emergency response – police, fire and ambulance – for assisting people,” he said.
A meeting of the government’s emergency cobra committee was due to be held on Tuesday afternoon.