Story highlights The teens are believed to have made it to war-torn Syria

The girls' parents publicly begged them to come home

(CNN) Three teen British girls suspected of traveling to Syria to join ISIS appeared on surveillance video in Turkey before they went to their destination.

Images show the teens boarding a bus in Istanbul, Turkish HBR television reported. It's the first sighting of the girls since they left London almost two weeks ago.

Authorities have said they have no reason to believe the girls are still in Turkey and believe they have crossed into neighboring Syria, parts of which have been taken over by Islamist terror group ISIS.

The three east London classmates -- Shamima Begum, 15; Kadiza Sultana, 16; and Amira Abase, 15 -- boarded a Turkish Airlines plane from London's Gatwick Airport to Istanbul on February 17.

A British counterterrorism officer said police had tried to reach out to the girls using the Turkish media and social media to persuade them to return home.