Though the extremely cautious nature of their statements means they didn’t offer much detail, the Organization for the Prohibition of Chemical Weapons (OPCW) is expressing “extreme concern” about the possibility that ISIS is not only using chemical weapons, but is making them.
The “possibility” is just their reluctance to confirm things they haven’t been formally authorized to confirm, as ISIS has bragged about their capacity to manufacture chemical weapons in multiple videos, and they have repeatedly launched such strikes, sickening large numbers of civilians and combatants.
ISIS has captured a large number of empty chemical weapons shells over the course of the war in Iraq and Syria, remnants of those nations’ since dismantled programs, and has developed the capability to produce some more primitive chemicals to deploy in such weapons.
Though far from the level of advanced chemical weapons that modern states would possess, the ISIS arms have proven extremely effective at fueling panic among their enemies. Even if they are of limited practical use on the battlefield, ISIS’ arsenal appears to be quite useful as a propaganda tool.
They have access to sarin precursors and are quite capable of making it.