BEIRUT (Reuters) - Tribal chiefs are organizing a way for Syrian Islamic State fighters to leave the Syria city of Raqqa after the U.S.-backed Syrian Democratic Forces agreed to a proposal that would secure their departure, the chiefs said in a statement sent to Reuters by a member of Raqqa s civil council. Saying their aim was to spare bloodshed, the tribal sheikhs said they had called on both the SDF and the U.S.-backed coalition fighting Islamic State to  settle the situation  of remaining Syrian fighters in the city, and to  secure their exit to areas outside the city with our guarantees .  