One of three London schoolgirls who travelled to Islamic State-controlled area of Syria to become "jihadi brides" is believed to have been killed in an air strike, a lawyer for her family says.

Canadian officials say they won't comment on matters of national security when faced with questions about a Canadian intelligence connection to a man accused of helping three British girls join ISIS.

Canadian government sources say an individual Turkish authorities accuse of helping three British girls cross into Syria is not a Canadian citizen and is not an employee of CSIS.