Chemical weapons expert say sulphur mustard was used in 2015 in an attack on Kurdish forces in Iraq blamed on Islamic State (IS) militants.
In August 2015, the Organisation for the Prohibition of Chemical Weapons (OPCW) was sent samples after 35 Peshmerga fighters became ill near Irbil.
On Monday, the sources say the samples tested positive for sulphur mustard.
If confirmed, it would be the first known use of chemical weapons in Iraq since the fall of Saddam Hussein.
OPCW experts recently concluded that sulphur mustard was used in August in neighbouring Syria, during fighting between Isis and rebel forces.
