Chemical protective gear
© AFP 2016/ JM LOPEZ
In 2013, a massive chemical weapons attack was carried out in the Syrian suburb of Ghouta which killed more than 1,300 civilians. Both the Syrian government and the militant factions that oppose it blamed one another for the attack.

"We assess that Syria has not declared all the elements of its chemical weapons program to the Chemical Weapons Convention (CWC)," Clapper stated. "Despite the creation of a specialized team and months of work by the Organization for the Prohibition of Chemical Weapons (OPCW) to address gaps and inconsistencies in Syria's declaration, numerous issues remain unresolved."

A mission to eliminate Syria's chemical arsenal was announced after the deadly 2013 gas attack. The Syrian government placed its chemical weapons under international control on Russia's urging.

Clapper also accused the Syrian government of continuing to use chemicals "as a means of warfare," and said he believed even non-state actors were using chemical weapons.