Independent aid group Medecins Sans Frontieres (MSF) reported Aug. 25 that it had treated four members of a Syrian family who suffered from breathing difficulties and developed blisters after a mortar hit their home in Marea, Aleppo governorate. The Syrian American Medical Society also reported receiving 50 patients showing symptoms of chemical exposure in the same area. Local rebels said the shells were fired from an ISIS-held village to the east. A spokesman for one rebel group, the Shami Front, told the New York Times that half of the 50 mortars and artillery rounds that hit Marea contained sulphur mustard. The powerful irritant and blistering agent —commonly known as "mustard gas" but actually liquid at ambient temperature—causes severe damage to the skin, eyes and respiratory system.

MSF said the four patients—two parents and their daughters, aged 3 and 5—arrived at one of its field hospitals an hour after the Aug. 21 attack, suffering from respiratory difficulties, inflamed skin, red eyes and conjunctivitis. Within three hours they developed blisters and their respiratory difficulties worsened. Staff gave them oxygen before transferring them to another facility for specialised treatment. "MSF has no laboratory evidence to confirm the cause of these symptoms," said MSF Syria program manager Pablo Marco. "However, the patients' clinical symptoms, the way these symptoms changed over time, and the patients' testimony about the circumstances of the poisoning all point to exposure to a chemical agent."

The Syrian American Medical Society said its field hospital in Marea had received more than 50 civilians who exhibited similar symptoms. Some 30 civilians developed skin blisters, with doctors identifying the agent to be sulphur mustard. The organization said samples had been taken from patient blood, clothing, and hair as well from the shelling site, to be assessed.

Earlier this month, the US military said ISIS was suspected of having used chemical agents in an attack on Kurdish forces at Makhmour in northern Iraq.  (BBC News, Aug. 25)

The Guardian wrote: "The evidence raises the prospect, denied by the Pentagon, that Isis has gained access to chemical stockpiles from Syrian president Bashar al-Assad's regime thought to have been destroyed or degraded. A 2013 accord, brokered by Russia, took Assad's declared chemicals out of Syria in an 11th-hour move to avert US bombing."

However, there have also been reports that ISIS has seized chemical materials in Iraq. Syria has seen several chemical attacks since the Assad regime supposedly surrendered its chemical stockpile.