A video has emerged that appears to show a man helping three British schoolgirls on their way to Syria from Turkey.
The footage is believed to show Shamima Begum, 15, Kadiza Sultana, 16, and Amira Abase, 15, in Gaziantep on the Turkish border with the war-torn nation.
They are seen wearing the same distinctive khaki, hooded winter coats, that they were wearing in an earlier video of them at a bus station in Istanbul.
Their sports holdalls are unloaded from the boot of one car before being transferred to another vehicle.
In the video from local news channel A Haber TV, a man speaking in English - who was later detained by Turkish authorities - appears to make mention of Syrian passports.
Turkish officials said the man was working for the intelligence service of a country that is part of the anti-Islamic State coalition, but did not publicly name the country.
The Foreign and Commonwealth Office (FCO) confirmed that a foreign spy had been detained on suspicion of helping the schoolgirls travel to Syria to join IS as "jihadi brides".
The nationality of the person arrested remains unclear, but the FCO and Met Police said they were working closely with the Turkish authorities.
Turkish foreign minister Mehmet Cavusoglu told reporters the detained suspect works for the intelligence agency of a country that is part of the US-led coalition against IS.
Shamima, Zadiza and Amira sparked an international manhunt when they flew from Gatwick to Istanbul on February 17.
The three girls paid more than £1,000 in cash to a travel agent for their flights to Turkey and police officers believe they stole jewellery from relatives to fund the trip.
A handwritten list seen by the Guardian newspaper, written in two different handwriting styles, appears to be show the how the girls prepared to join Islamic State. The list includes the French word for 'ticket', with a quote for around £1,000 for flights to Turkey. The total cost is listed at more than £2,000.
Items on the list include a £50 epilator, sets of underwear for £12, socks, a mobile phone, make-up, new boots and a new bra. Different handwriting lists the costs of travel, including the costs of visas, a coach, a taxi and a hotel room, as well as how much cash to bring, according to the Guardian's report.
Scotland Yard was forced to admit at the weekend that the families had not been informed that a 15-year-old fellow student at the three girls' school had gone to the war-torn country, but rather only that she had gone missing.
That first girl who travelled to Syria was named on Saturday by the Mail as 15-year-old Sharmeena Begum. Her father said his daughter became religious after losing her mother to cancer.