Police have arrested a 25-year-old woman on suspicion of preparation of terrorist acts in connection with Syria, Scotland Yard has said.
Counter-terrorism officers took the young woman from Bedfordshire to a central London police station, where she remains in custody.
Two addresses in Bedfordshire were being searched as part of the investigation.
Police said the investigation is related to Syria.
The arrest comes after four men appeared in court last week charged with terrorism offences. Details of the charge included swearing allegiance to Isis, who have seized large swathes of Syria and Iraq, and conducting “hostile reconnaissance" on policemen or soldiers on the streets of London.
On Tuesday, London police chief Bernard Hogan-Howe said at least five Britons were travelling to Iraq and Syria every week to fight for the militant group, with some 500 Britons believed to have already travelled to the region to join the fighting.
Mark Rowley, Britain's national policing spokesman for counter-terrorism, said police had made 218 arrests this year and that detectives were carrying out security investigations at an "exceptionally high" pace not seen in years.
Additional reporting by the Press AssociationReuse content