CIA reports have said that over the past four decades Syria has amassed huge supplies of mustard gas, sarin nerve agents and cyanide "which can be delivered by aerial bombs, ballistic missiles and artillery rockets".
A CIA report in 2006 said that Syria "is developing the more toxic and persistent nerve agent VX".
Globalsecurity.org says "exact volumes of weapons in the Syrian stockpile are difficult to know. The CIA has estimated Syria to possess several hundred litres of chemical weapons with hundreds of tonnes of agents produced annually".
It says, "Syria is significantly dependent upon outside assistance for all of its WMD programmes. There have been reports over the life of the Syrian programme that Syria has obtained significant assistance from various states, significantly Russia and France."