Leaders of countries affected by recent terror attacks have voiced solidarity with the UK after the deadly attack near the Houses of Parliament.
Leaders of France and Germany, which suffered deadly vehicle attacks last year, offered the UK their support.
The US president offered condolences and praised UK security forces.
Among the 40 people injured by the car on Westminster Bridge are three French schoolchildren and two Romanians. In Paris, the lights of the Eiffel Tower went out from midnight (23:00 GMT) in a tribute to the victims.
