A British woman has been arrested by counter-terror officers at Luton Airport, police have said.
Scotland Yard said the 21-year-old was detained at 11.15 am on Thursday after landing on a flight from Istanbul, The Telegraph reported on Thursday.
She was arrested on suspicion of preparation of acts of terrorism and was taken into custody at a police station in south London.
The development follows the arrest of a 19-year-old man and two 17-year-old boys, from north-west London, on Saturday on suspicion of preparing terrorist acts.
They were later bailed, as was an 18-year-old arrested by counter-terrorism officers from West Midlands Police on Monday.
The latest arrests came only weeks after three east London schoolgirls - Kadiza Sultana, Amira Abase and Shamima Begum - ran away to become so-called “jihadi brides”.