Mustard gas was used in two attacks in Iraq's semi-autonomous Kurdish region in August last year, according to sources close to the global chemical-weapons watchdog.
Sources told AFP and Reuters on February 15 that an investigation by The Hague-based Organization for the Prohibition of Chemical Weapons (OPCW) had confirmed the use of mustard gas.
The sources said the deadly gas, which was banned globally in 1925, was used on August 11 on the towns of Gweyr and Makhmur located southwest of Irbil, capital of the Kurdistan region.
The revelation comes days after U.S. officials said that Islamic State (IS) militants had the capability to make small quantities of chlorine and mustard gas and had used it in Iraq and Syria.
It is unclear who used the chemical, although Kurdish officials said in October 2015 that several of its troops had tested positive for mustard gas after battles in August with IS fighters.
OPCW confirmed it had sent a team of experts to help Iraq in its investigation into possible chemical weapons.