Union flags fly at half-mast in London on Thursday as police maintain a security cordon
Union flags fly at half-mast from Portcullis house and the Houses of Parliament on Thursday
A Twitter picture shows a car on the sidewalk in front of the Palace of Westminster
A police security cordon remains around the Houses of Parliament in London
Forensic officers work at the scene of the attack by the Houses of Parliament in London
Armed police officers patrol outside New Scotland Yard in London on Thursday
Deputy Acting Commissioner Mark Rowley speaks to media outside New Scotland Yard
Police officers and forensics investigators work on Westminster Bridge
An armed police officer stands on Whitehall the morning after an attack in London
British Prime Minister Theresa May speaks outside 10 Downing Street in central London
The Great Clock of the Elizabeth Tower, better known as Big Ben, is pictured in London
The lights of the Eiffel Tower are switched off at midnight in solidarity with the city of London