Two people have been arrested at Heathrow Airport on suspicion of committing terrorism offences.
A man and a woman were held at 8.30pm on Tuesday after arriving on a flight from Egypt into the airport.
The pair, both aged 26, were arrested by officers from the Metropolitan Police's Counter Terrorism Command on suspicion of the commission, preparation or instigation of acts of terrorism.
They were taken to a central London police station, where they remain in custody.
In recent months concerns have been raised that foreign nationals are travelling to Syria with the intention of supporting jihadist movements.
In August, Khalid Mahmood, Labour MP for Birmingham Perry Barr, said a number of people in his constituency were travelling to the war-torn Middle Eastern state, and that he expected this to increase.
The nationalities of the arrested pair have not yet been released, but they are not Egyptian.
Two addresses being searched in east London are residential, Scotland Yard said.