Syrian civilians receive treatment after an alleged poisonous gas attack fired by regime forces, according to activists in Arbeen, Syria, near Damascus, on Wednesday, Aug. 21, 2013, in this citizen journalism image provided by the Local Committee of Arbeen and authenticated on its contents and other AP reporting. (AP Photo/Local Committee of Arbeen)

Photo by: HOEP

Syrian civilians receive treatment after an alleged poisonous gas attack fired by regime forces, according to activists in Arbeen, Syria, near Damascus, on Wednesday, Aug. 21, 2013, in this citizen journalism image provided by the Local Committee of Arbeen and authenticated on its contents and other AP reporting. (AP Photo/Local Committee of Arbeen)