Police have arrested a woman as she arrived at Heathrow Airport on suspicion of preparing acts of terror.
The 21-year-old, from north London, had just landed in the UK following a flight from Istanbul, Turkey.
Scotland Yard reported that the woman, who was detained on Thursday, was suspected of carrying out Syria-related offences.
She is currently being held at a south London police station.
Two searches of addresses north of the capital have since been carried out.