"On August 18, the Organization for the Prohibition of Chemical Weapons (OPCW) announced the complete destruction of Syria's declared chemical weapons (CW). Despite this significant achievement, serious challenges relating to Syrian CW remain. In early September, the Syrian regime announced previously undeclared chemical weapons research facilities, raising questions about what else it might be concealing. Repeated reports have alleged chlorine gas attacks by the Assad regime. Moreover, press reports speculate that insecure chemical weapons stocks in Syria and Iraq may have gotten into the hands of the Islamic State (ISIL). Most of these questions cannot yet be answered definitively, but the fate of Syria's CW capabilities warrants continued attention. Syria's CW program began in the 1970s with help from the Soviet Union, primarily as a hedge against Israel. After joining the Chemical Weapons Convention (CWC), Syria declared 1,300 metric tons of chemical warfare agents and precursor chemicals, including several hundred metric tons of the nerve agents sarin and VX [O-ethyl S-(2-diisopropylaminoethyl) methylphosphonothiolate or Methylphosphonothioic acid], as well as mustard agent in ready-to-use form. The nerve agents were stored as two separate components that are combined before use, a form that facilitated removal and destruction efforts."
CRS Insight, IN10160