The global chemical weapons watchdog has found after a nearly two-year investigation that at least one Syrian military helicopter dropped gas cylinders onto residential buildings in the rebel-held Syrian city of Douma in 2018, killing 43 people.
The April 7, 2018, attack on the outskirts of Damascus was part of a major military offensive that returned the area to the control of forces under Syrian President Bashar al-Assad after a prolonged Russian-backed siege against the rebel stronghold.
A previous investigation by the Organisation for the Prohibition of Chemical Weapons (OPCW) had already concluded in March 2019 that a chemical attack had taken place in Douma, but that inquiry had not been mandated to assign blame.
The Investigation and Identification Team was established by member states at the Hague-based OPCW in November 2018 to identify perpetrators of chemical attacks in Syria after Russia vetoed the joint UN-OPCW mission.
Syria denies using chemical weapons but a previous joint inquiry of the United Nations and the OPCW found that the Syrian government used the nerve agent sarin in an April 2017 attack and has repeatedly used chlorine as a weapon.
It blamed Islamic State militants for mustard gas use.
The latest inquiry identified four alleged perpetrators in one air force unit, but their names were not made public.
Toxic gas dropped on civilian area
The findings are based on technical analysis of 70 biological and environmental samples, satellite imagery, 66 witness interviews and ballistic and munitions testing, the OPCW said.
"At least one helicopter of the Syrian Tiger Forces' Elite Unit dropped two yellow cylinders containing toxic chlorine gas on two apartment buildings in a civilian-inhabited area in Douma, killing 43 named individuals and affecting dozens more," a summary of the report said.
The Tiger Forces are elite Syrian troops generally used in offensive operations in the war.
“The use of chemical weapons in Douma – and anywhere – is unacceptable and a breach of international law,” OPCW director-general Ambassador Fernando Arias said.
"The world now knows the facts," he said.
"It is up to the international community to take action, at the OPCW and beyond."
The findings follow an investigation conducted between January 2021 and December 2022.
The conclusions were "reached on the basis of 'reasonable grounds', which is the standard of proof consistently adopted by international fact-finding bodies and commissions of inquiry", the OPCW said.
Syria failed to cooperate with OPCW
The OPCW's identification team is deeply opposed by Syria and its military ally, Russia, who say it is illegal. Damascus and Moscow did not cooperate with the latest investigation.
Both countries have denied using banned toxic munitions and have instead said the attack in Douma was staged.
Several Russian-backed theories about the attack were tested but could not be substantiated, the team found.