The world ' s chemical weapons watchdog has determined that mustard gas was used over two months ago in a Syrian town, an official from that group said, raising fresh questions about the deployment of such weaponry in the country's bloody, messy war. The August 21 incident in Marea, a town about 28 miles (45 kilometers) north of Aleppo, exposed at least two people "to sulfur mustard, and there is reason to believe that a baby might have also suffered and died as a result," according to an official with the Organization for the Prohibition of Chemical Weapons. The report doesn't assign blame and even mention any force involved in Syria's messy, years-long civil war -- including ISIS, the terrorist group that's taken over swaths of the country, or fighters loyal to President Bashar al-Assad. "It's very serious because mustard gas is a known chemical weapon," the OPCW official said. "It's obviously very, very dangerous and extremely toxic, so it's a new level of concern." Chemical weapons have been a major storyline in Syria's war, with international forces accusing Assad's forces of using them against civilians. Faced with such allegations -- not to mention threats of direct force by world powers -- Assad's government agreed in 2013 to give up and turn over its chemical weapons stockpiles. That deal was brokered by the United States and Russia, and then signed off on by the United Nations Security Council. The OPCW -- the body in charge of overseeing the process -- confirmed in June of last year that the final stockpile had been removed. That's why fresh claims of such use are such a big deal whether used by the Assad regime or by militant groups, such as ISIS.