The Secretariat of the Organisation for the Prohibition of Chemical Weapons (OPCW)'s fifth report concludes there are reasonable grounds to believe that the Syrian Arab Air Forces were the perpetrators of the chemical weapons attack on 1 October 2016 in Kafr Zeita in the Syrian Arab Republic. The comprehensive investigation was conducted by the Investigation and Identification Team (IIT) from March 2024 to December 2025.
Based on the analysis and corroboration of the all obtained information, the Secretariat concludes there are reasonable grounds to believe the Syrian Arab Air Force dropped at least one yellow pressurised cylinder, which hit a cave system in the Wadi al-Aanz valley in Kafr Zeita. The pressurised cylinder impacted near two ventilation openings near the Al Maghara Hospital. The cylinder then tumbled down and came to rest near the entrance of the cave system. Upon impact, the cylinder ruptured and pressurised released chlorine gas, dispersing through the Wadi al-Aanz valley, injuring 35 named individuals and affecting dozens more.
The Secretariat reached its conclusions based on the standard of proof known as "reasonable grounds", a standard consistently adopted by international fact-finding bodies and commissions of inquiry. The assessment included information from the Fact-Finding Mission (FFM), States Parties, interviews conducted by the IIT, and analyses of samples, computer modelling, satellite imagery, front-line maps, authenticated videos and photos, and other relevant data. This information was considered holistically and OPCW procedures were strictly adhered to. The Secretariat also thoroughly considered the positions put forward by the former Syrian authorities but was unable to obtain any concrete information supporting those positions. To date, five reports identifying perpetrators have been issued by the OPCW on seven cases of use of toxic chemicals as weapons in Syria.
OPCW Director-General Ambassador Fernando Arias said: "We welcome the assistance received from the new Syrian authorities, marking the first cooperation by the Syrian Arab Republic with an IIT investigation. These actions are in line with the commitments made by President Ahmad al-Sharaa, when I visited Damascus in February last year. This represents a significant milestone and a meaningful contribution to international accountability."
"This new report provides further evidence of a pattern of systematic use of toxic chemicals as weapons by the former Syrian authorities against their own people. The report and its findings are now in the hands of the international community, the United Nations, and the States Parties to the Chemical Weapons Convention. The Secretariat will continue its investigations to identify perpetrators of chemical weapons use in Syria through its Office of Special Missions," he added.
Background
Syria acceded to the Chemical Weapons Convention (CWC) in 2013 under a stringent verification regime. While Syria submitted an initial declaration of its chemical weapons (CW) programme, the former Syrian government did not declare all its CW programme and attempted - unsuccessfully - to mislead the international community about the overall scope and scale of the Syrian chemical weapons programme. Furthermore, the Technical Secretariat documented and independently confirmed chemical weapons use in Syria both by the former Syrian military forces and by non-state actors, specifically ISIS/ISIL.
The fall of the Assad government in December 2024 created an opportunity to uncover the full scope of Syria's chemical weapons programme and to eliminate it in line with the CWC. In February 2025, the OPCW Director-General visited Syria and held separate meetings with the Syrian President and Foreign Minister. They expressed Syria's recognition of all OPCW mandates, including the identification of perpetrators of chemical weapons use in Syria and reaffirmed Syria's full commitment to fulfilling its obligations under the CWC. In March 2025, the Syrian Foreign Minister visited the OPCW and addressed the Executive Council, where he renewed Syria's commitment to the Convention.
Since the visit by the Director-General to Damascus in February 2025, the OPCW Technical Secretariat deployed several times to Syria, involving visits to suspected locations, sampling, interviews, collection of documents related to Syria's chemical weapons programme, and coordination.
Since November 2025, OPCW has re-established a continuous presence in Syria to facilitate upcoming inventory, destruction and verification-related activities. The work related to the Syrian chemical weapons dossier - verification of declarations and investigation of use of toxic chemicals as weapons - is now coordinated by the OPCW Office of Special Missions.
As the implementing body for the Chemical Weapons Convention, the OPCW, with its 193 Member States, oversees the global endeavour to permanently eliminate chemical weapons. Since the Convention's entry into force in 1997, it is the most successful disarmament treaty eliminating an entire class of weapons of mass destruction.
In 2023, the OPCW verified that all chemical weapons stockpiles declared by the 193 States Parties to the Chemical Weapons Convention since 1997 - totalling 72,304 metric tonnes of chemical agents - have been irreversibly destroyed under the OPCW's strict verification regime.
For its extensive efforts in eliminating chemical weapons, the OPCW received the 2013 Nobel Peace Prize.
