Two 17-year-old boys from north west London and a 19-year-old man detained by Turkish authorities Istanbul were returned to the UK yesterday and are now in a central London police station.
Turkish officials believe that they were planning to travel across the border to join militant group Isis, also known as Islamic State, reports Reuters.
The Metropolitan Police's Counter Terrorism Command (CTC) have now arrested all three males on suspicion of preparation of terrorist acts.
None of them have yet been charged.
Police were made aware that the teenagers intended to travel to Syria and alerted the Turkish authorities who were able to intercept them before crossing the border.
GCSE pupils Amira Abase, 15, Shamima Begum, 15, Kadiza Sultana, 16, are now believed to have reached Isis's de facto capital of Raqqa, in Syria.
CCTV footage has since emerged, showing the three girls waiting for a bus to the Syrian border. An interpreter can be heard saying "take the Syrian passports, one, two, three", before adding, "it's nice" as a car can be heard driving off.
A fourth girl - who attended Bethnal Green Academy with the girls who went missing in April - who left in December and is believed to have left to become a Jihadi bride was named last week by police as 15-year-old Shermeena Begum.
