The Organization for the Prohibition of Chemical Weapons (OPCW) recently confirmed that laboratory tests of samples taken following Daesh attacks on Kurdish forces southwest of Erbil in August 2015 tested positive for sulphur mustard. (see Reuters dispatch by Anthony Deutsch, "Exclusive: Samples confirm Islamic State used mustard gas in Iraq - diplomat" < http://mobile.reuters.com/article/idUSKCN0VO1IC >)
Reuters reported that a OPCCW representative "speaking on condition of anonymity because the findings have not yet been released, said the result confirmed that chemical weapons had been used by Islamic State fighters."
This is the second documented use by Daesh/ISIS forces following tests that confirmed use of mustard gas by Daesh/ISIS forces in Syria.
As the Reuters dispatch also points out, the precursors and technology to make these weapons are easy enough to find or create in oil producing regions, and so it is possible ISIS is developing them de novo. More ominous would be if new weapons are be created from remnants of Syria’s former stockpile because it would mean faulty accounting for the weapons supposedly dismantled under international supervision back in 2014.
The Syrian stockpile was allegedly dismantled under international supervision as part of a deal to avoid potential US/UN intervention following the use of Sarin nerve gas by forces loyal to Syrian President Bashar al-Assad against a rebellious area near Damascus in 2013. Assad denied he authorized use of chemical weapons. (more)