BEIRUT (Reuters) - Some, but not all, foreign Islamic State fighters have left Syria s Raqqa city on Sunday as part of a withdrawal deal with U.S.-backed militias, a local official told Reuters on Sunday.  Omar Alloush, a member of the Raqqa Civil Council, would not say how many militants remain in the city, where the U.S.-backed Syrian Democratic Forces have hemmed them into a small enclave.  An SDF spokesman said earlier that a group of Syrian Islamic State fighters without foreign militants had evacuated Raqqa overnight, taking civilians with them as human shields. 