London police fear that three "straight-A" students may have hopped a flight to Istanbul with plans to cross into Syria and join ISIS. Shamima Begum, 15, Kadiza Sultana, 16, and a third girl whose name has not been released, also 15, reportedly took off Tuesday.

The girls, all classmates at the Bethnal Green Academy in East London, boarded an early flight to Turkey on Tuesday and haven't been heard from since. From the Guardian:

Counter-terrorism officers said the three girls left their homes before 8am last Tuesday providing their families with plausible reasons as to why they would be out for the day. One of the girls told her family she would be studying.

Instead they met and travelled to Gatwick airport. They boarded a Turkish Airlines flight, TK1966, which departed at 12:40pm to Istanbul, Turkey and landed at 6:40pm local time.

Walton said it was possible that the girls have not yet travelled far from Istanbul, given the snowy weather conditions in the Turkish city, but they are thought to be intending to go to Syria.

Shamima, police say, might be posing as her sister, Aklima Begum, using her passport to travel.

Commander Richard Walton, head of the London Metropolitan Police's counterterrorism unit, told the Telegraph that the teens are "good friends" with a girl who ran away to Syria in December to join the Islamic State, and are apparently seeking to join her.

[Image via London Metropolitan Police]