Nine young British medical students travelled illegally to Syria and are believed to be working in hospitals in Daesh-controlled areas, British media sources said.
A report issued by the Guardian newspapers said that the group of four women and five men crossed into Syria from Turkey last week and traveled from Sudan where they had been studying.
British Security services estimated that some 600 Britons have gone to Syria or Iraq to join militant groups, including the man known as "Jihadi John" who has appeared in several Daesh beheading videos.