Banned chlorine munitions were likely dropped on a Syrian neighbourhood in February, an international body on chemical weapons said, after laboratory tests confirmed the presence of the toxic chemical.
In its latest report on the systematic use of banned munitions in Syria's civil war, the Organisation for the Prohibition of Chemical Weapons (OPCW) did not say which party was behind the attack on Saraqib, which lies in rebel-held territory in the province of Idlib.
But witnesses told OPCW investigators that the munitions were dropped in barrel bombs from a helicopter, a report released by the OPCW showed. Only Syrian government forces are known to have helicopters.
The report by the OPCW's fact finding mission for Syria "determined that chlorine was released from cylinders by mechanical impact in the Al Talil neighbourhood of Saraqib."
About 11 people were treated after the attack on Feb. 4. for mild and moderate symptoms of toxic chemical exposure, including breathing difficulties, vomiting and unconsciousness, the report said.
A joint OPCW-U.N. mechanism for Syria has previously concluded the Syrian government has used both sarin nerve agent and chlorine, killing and injuring hundreds of civilians.
The government of Syrian President Bashar al-Assad has denied using chemical weapons and instead has blamed rebels for staging attacks to falsely implicate his forces in the atrocities.
The mechanism was disbanded in November following a Russian veto at the U.N. Security Council, a move which ratcheted up tension between Moscow and Western powers over chemical weapons use in Syria.