An 18-year-old woman has been arrested at Stansted airport on suspicion of terror offences.
Counter-terrorism officers arrested the teenager as she left a flight at the airport in Essex at around 4pm on Friday, Scotland Yard said.
Officers then took her to a police station in central London, where she remains in custody.
Police said they detained her on suspicion of preparation of terrorist acts and membership of a forbidden organisation.
As part of the same investigation, a 21-year-old man was arrested in Hackney, north east London, on Wednesday 29 October.
Police arrested him on suspicion of assisting another to commit acts of terrorism, or to engage in any conduct for the committing of such acts, by facilitating another to travel abroad.
He was taken to a south London police station, where he was later bailed to return to on a date in late December.
He has since been re-bailed to a date in January.
A search at the residential address in Hackney was also carried out.
Additional reporting by PAReuse content