Two men from Birmingham have been arrested on suspicion of terrorism offences relating to activities in Syria.
The men, both aged 21, were detained at Heathrow airport after flying in from Istanbul. Both men were taken to a police station in the West Midlands area where they continue to be questioned.
Officers believe the men had travelled to Syria last May. Police reassured that there is no immediate threat to the public and the allegations relate to their time in the Arab country.
Det chief Supt Kenny Bell, head of the West Midlands Counter Terrorism Unit, said: "We took action in order to ensure we can properly understand what activities these men have been engaged in whilst in Syria − not because they posed any imminent threat to the public."
European officials are concerned about domestic threats posed by fighters returning from Syria. British intelligence officials say they have seen "low hundreds of people" from Britain go to Syria to fight.
A handful of people have been arrested in the UK on suspicion of attending terrorism training camps in Syria.