Insurgents in Syria used sulfur mustard in August, which probably resulted in the death of an infant, the Organization for the Prohibition of Chemical Weapons said Friday. The organization’s statement was the first official confirmation that sulfur mustard, often called mustard gas, has been used by insurgents in Syria. Inspectors found evidence of sulfur mustard use by insurgents in the town of Marea on Aug. 21, the organization said, and Friday’s official confirmation shows another worrying escalation in Syria’s brutal civil war, which has already killed 250,000 people and forced millions to flee. “In this case, the team was able to confirm with utmost confidence that at least two people were exposed to sulfur mustard, and that it is very likely that the effects of this chemical weapon resulted in the death of an infant,” the organization said. It is not clear how insurgents came to possess sulfur mustard.