Turkish foreign minister Mehmet Cavusoglu earlier said the suspect works for the intelligence agency of a country that is part of the US-led coalition fighting ISIS but did not identify the country, saying only that it was not the United States or a member of the European Union.

However, an Istanbul-based newspaper has reported that the spy was working for the Canadian government.
Mr Cavusoglu, who was interviewed on Turkish channel A Haber TV, said he had shared the information with his British counterpart - Foreign Secretary Philip Hammond.

Shamima Begum, Amira Abase, both 15, and Kadiza Sultana, 16, are thought to have reached the terror group's de facto capital Raqqa after fleeing the UK to join a friend last month.

Britain's Foreign Office had no immediate comment and a spokesman for the Metropolitan police said he had no information.

At least 22 young women, the vast majority under the age of 20, are feared to have travelled to Syria from the UK over the past 12 months.