British media on Monday reported that Turkish hostages freed by the Islamic State in Iraq and Syria (ISIS) group last month may have been released as part of a prisoner exchange for up to 180 jihadist fighters.
The Times newspaper cited a list it had received saying that among the fighters were three French nationals, two British, two Swedes, two Macedonians, one Swiss and one Belgian.
It said the list had been confirmed by its ISIS sources.
The BBC cited a Whitehall source saying the report was "credible".
The Times report named the two British nationals as 18-year-old Shabazz Suleman and 26-year-old Hisham Folkard.
It did not say how the men had come into Turkish custody.
The report cited a spokesman for a group involved in the deal saying the exchange also included relatives of Abu Bakr al-Iraqi, a senior ISIS member killed by Syrian rebels in January.