Official on the mission says Syrian rebel group may have used nerve gas . Peter Bergen : It would not be first time al Qaeda - affiliated group used chemical weapons . Chlorine gas was used by both sides during World War I but was banned by the Geneva Protocol , along with the use of other poison gases , after the end of the war . Obama administration raises allegations that rebels used chemical weapons . CIA : Issue of who may have used them in Syria is key to further investigation .
Official on the mission says Syrian rebel group may have used nerve gas . Peter Bergen : It would not be first time al Qaeda - affiliated group used chemical weapons . Obama administration raises allegations that rebels used chemical weapons . CIA : Issue of who may have used them in Syria is key to further investigation .