Syrian forces have used chemical weapons more than two dozen times during the country's civil war, including in the deadly attack that led to US air strikes on regime planes, UN war crimes investigators said on Wednesday.
In the most conclusive findings to date from investigations into chemical weapons attacks during the conflict, the UN Commission of Inquiry on Syria said a regime warplane dropped sarin on Khan Sheikhoun in Idlib province in April, killing more than 80 civilians and injuring almost 300.
"Government forces continued the pattern of using chemical weapons against civilians in opposition-held areas. In the gravest incident, the Syrian air force used sarin in Khan Sheikhoun, Idlib, killing dozens, the majority of whom were women and children," the report said, declaring it a war crime.
The attack was previously identified as containing sarin, an odourless nerve agent. But that conclusion, reached by a fact-finding mission of the Organisation for the Prohibition of Chemical Weapons (OPCW), but stopped short of saying who was responsible.
In all, UN investigators said they had documented 33 chemical weapons attacks to date.
Twenty-seven were by President Bashar al-Assad's forces, including seven between March 1 to July 7. Perpetrators had not been identified yet in six early attacks, they said.
The Assad regime has repeatedly denied using chemical weapons. In the deadliest Khan Sheikhoun attack, Russian and Syrian officials denied that Syrian forces had used chemical weapons, explaining that air strikes conducted by Syrian forces that day had struck a terrorist chemical weapons depot.
"As the result of an aerial campaign by pro-Government forces in the area surrounding Khan Shaykhun, many medical facilities were destroyed, which compounded the suffering of victims of the sarin attack," the report added.
In Idlib, Hamah and eastern Ghouta, Syrian forces also used weaponised chlorine.
According to independent monitors, hundreds of thousands of civilians have been killed in the war, mostly by the regime and its powerful allies, and millions have been displaced both inside and outside of Syria.
As well as the use of chemical weapons, brutal tactics pursued mainly by the regime have included sieges, mass executions and torture against civilians, leading to war crimes investigations.