WASHINGTON Islamic State militants are believed to be responsible for sulphur mustard gas attacks in Syria and Iraq last year, the United States said on Wednesday.

WASHINGTON Islamic State militants are believed to be responsible for sulphur mustard gas attacks in Syria and Iraq last year, the United States said on Wednesday.

State Department spokesman Mark Toner said Islamic State insurgents were responsible for a mustard gas attack in the town of Marea on Aug. 21 "largely based on photographic evidence as well as Syrian opposition description of the event."

A confidential Oct. 29 report by the Organization for the Prohibition of Chemical Weapons, or OPCW, concluded that at least two people were exposed to sulphur mustard in Marea, north of Aleppo, in August.

Syria is supposed to have completely surrendered the toxic chemicals 18 months ago. Their use violates United Nations Security Council resolutions and the 1997 Chemical Weapons Convention.

Toner also said that based on available information, the United States believed that the Islamic State group was responsible for mustard gas attacks in Iraq. It is the first known use of chemical weapons in Iraq since the fall of Saddam Hussein.

A source at the OPCW confirmed that laboratory tests were positive for sulphur mustard after 35 Kurdish troopers were sickened on the battlefield in August.

Sulphur mustard is a Class 1 chemical agent, which means it has very few uses outside chemical warfare. Used with lethal effectiveness in World War One, it causes severe delayed burns to the eyes, skin and respiratory tract.

(Reporting by Lesley Wroughton; Editing by Toni Reinhold)

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