A man has been arrested at Luton Airport on suspicion of a terrorism offence after arriving on a flight from Turkey, police have said.
The 24-year-old was arrested after landing in the UK on Monday as part of an investigation by the Metropolitan Police's Counter Terrorism Command.
Scotland Yard said he was arrested on suspicion of membership of a proscribed organisation under section 11 of the Terrorism Act 2000.
The man was taken into police custody and later released under investigation, police said.
Officers' inquiries were said to be continuing.