Two men have been arrested on suspicion of terrorism offences after their car was stopped along Pall Mall in central London, police have said.
The pair, both 34 and from east London, were spotted acting suspiciously in a vehicle in Westminster at around 12.10am on Thursday and were stopped by armed officers in Pall Mall, according to the Metropolitan Police.
They were arrested under the Terrorism Act and taken to a police station where they are still being held.
No guns were fired and a counter-terror investigation has been launched, the force added.
Head of the Met's counter terrorism command, Commander Richard Smith, said: "Every day, police officers are on patrol across the capital, watching for suspicious behaviour and stopping people they suspect may be involved in criminality.
"Following the increase to the UK threat level from terrorism last week - as a precautionary measure - I would like to emphasise that the public should be alert but not alarmed."