The Islamic State (ISIS) in Syria has been producing chemical weapons and using them on Iraqi Kurds, according to a report by the Organization for the Prohibition of Chemical Weapons.
This marks the first known use of chemical weapons by a terrorist organization in more than 20 years.
Mustard gas was confirmed in samples from two separate sites in northern Iraq, where it had been used against Kurdish fighters near the city of Arbil.
The report comes just days after the US revealed that ISIS is capable of producing chemical weapons like chlorine and mustard gas.
National Intelligence chief James Clapper informed a congressional committee last week that ISIS had begun using chemical weapons in both Iraq and Syria.
Peshmerga fighters from the autonomous Kurdish region in north Iraq confirmed that ISIS had fired artillery shells containing chemical weapons, wounding dozens.
AFP contributed to this report.