80 Islamist jihadists were handed over to Islamic State in Iraq in exchange for 49 Turkish prisoners who were freed last month, according to the London-based Sunday Times.
Two Britons were among the fighters released by Turkey in the prisoner swap deal, according to the report.
49 hostages, including diplomats, soldiers, officers and their families, were abducted from Turkey’s Mosul consulate when Islamic State militants seized control of the Iraqi city in June.
Apart from the British men, identified by the Times as Shabazz Suleman, 18, and Hisham Folkard, 26, other Western militants were handed over to Islamic State, including three French citizens, two Swedish citizens, two Macedonians, one Swiss and one Belgian.
British counter-terrorism units were allegedly looking into the two men.
The newspaper said it obtained a list of fighters names that were traded for the Turkish nationals.
Turkish President Recep Tayyip Erdogan said at the time the release was part of a pre-planned operation by the nation's intelligence agency.