U.S. intelligence agencies suspect that Syrian President Bashar Al-Assad kept some of the chemical weapons or components that he agreed to surrender under a 2013 U.S.-Russian deal, an intelligence official told Reuters on Thursday.
"We have never taken the Assad regime at its word that it declared its entire chemical weapons stockpile," said the U.S. intelligence official, who spoke on condition of anonymity.
"Assad has repeatedly shown that he is willing to use whatever chemical weapons he has retained or reconstituted to attack and terrorize his own people," the official added.
Under the 2013 deal, Syria agreed to hand over its chemical stockpile to the Organization for the Prohibition of Chemical Weapons (OPCW) for destruction.
Last January, the OPCW said that Syria's declared chemical weapons arsenal has been completely destroyed, but even since that time, the global body has determined that chemical weapons have been "systematically and repeatedly" used as a weapon in Syria.
Officials believe sarin gas was used in this week's chemical weapons attack on the Idlib province.
The OPCW had in the past voiced "grave concern" at the continued use of toxic arms in Syria, calling for those behind such attacks to be held accountable.
Syria has denied ever using chemical weapons in the civil war, and it argues that claims otherwise or only meant to " serve political agendas".