The Organization for the Prohibition of Chemical Weapons (OPCW) on Monday voiced "serious concern" over reports that the Islamic State (ISIS) group has used chemical weapons in Iraq.
"Recent reports of possible use of chemical weapons in Iraq by non-State actors are a matter of serious concern," The Hague-based OPCW said in a statement quoted by the AFP news agency.
German officials said last week that Kurdish fighters had been attacked on Tuesday with chemical weapons, possibly chlorine or mustard gas, in northern Iraq, leaving many peshmerga suffering from "respiratory irritation.
The allegations, deemed "plausible" by an American official, follow claims in March by the autonomous Kurdish government in northern Iraq which said it had evidence that the jihadist group used chlorine in a car bomb attack on January 23.
The Wall Street Journal last week cited U.S. officials as saying they believe last week's attack used mustard gas, which may have come from stockpiles of banned poisons that Syrian President Bashar Al-Assad was forced to get rid of after joining the OPCW in 2013.
Officials who spoke to CNN late last week said that the United States government has test results from an ISIS attack in Hasakah, Syria, that confirm the terror group used a mustard agent as a weapon. The Iraq attack was still being investigated, they said.
The OPCW said it was in contact with the Iraqi government and "will examine any substantive reports it receives", according to AFP.
Along with the January attack, the Conflict Armament Research group and Sahan Research group said last month that ISIS had also targeted peshmerga with a projectile filled with an unknown chemical agent on June 21 or 22.
The chemical used had characteristics and clinical effects "consistent with a chlorine chemical agent", the groups said.
Information regarding the use of mustard gas by ISIS is relatively new. U.S. intelligence agencies have said in the past they believed the group has used chlorine gas in attacks in Iraq, though chlorine is not a banned chemical agent.