BBC News reports activists in Syria have published what they say is evidence of a chlorine gas attack by government forces. Footage posted online, which cannot be verified, shows medics trying to revive four young men suffering what appear to be symptoms of poisoning. A voice off-screen says the location is Harasta, just outside the capital Damascus. Use of chlorine as a weapon of war is banned and Syria committed to declaring and giving up its stocks last year. The face of one of the men in the video appeared to be covered in vomit, as he shook and moaned while doctors treated him. It is the fourth chemical weapons attack the opposition has alleged this month.