Shamima Begum, 15, Kadiza Sultana, 16, and 15-year-old Amira Abase sparked a police hunt after they flew to Istanbul from Gatwick Airport a week ago.
Scotland Yard last night said counter-terrorism officers leading the investigation "now have reason to believe that they are no longer in Turkey and have crossed into Syria," TASS cited the statement.
Police believes that they may have been recruited by jihadists on the internet.
