Turkey said on Sunday that three British teenagers allegedly trying to join the Islamic State (IS) militant group in Syria were detained in a Turkish airport and sent back to Britain.

The teenagers arrived at the Ataturk Airport in Istanbul through Spain. Turkish intelligence officers spotted the trio and identified as Gafur H, Muhammed N. and Muhammed Abdulla H, Xinhua reported.

Turkish and British police have intensified their cooperation after three British girls went missing from East London in early February and reportedly arrived in Turkey to cross into Syria.

Police in London said they had been made aware that two 17-year-old boys had gone missing and were thought to be travelling to Syria. Further inquiries revealed they had traveled with a 19-year-old male.

Three British schoolgirls entered Turkey last month and are thought to have joined the IS group in Syria.

On Thursday, the Turkish foreign minister said the girls had been helped to cross the border by a spy working for one of the country’s in the US-led coalition against the militants.

The Turkish police intelligence group has monitored more than a thousand people arriving in Turkey this year, and sent nearly half of them back to their countries.