Sarin or a similar banned toxin was used in the Khan Sheikhoun chemical weapons attack, the global chemical weapons watchdog has confirmed.
It was widely suspected that the nerve agent was used in the 4 April attack, which killed at least 87 people in the northern Syrian province of Idlib, and that was the conclusion reached earlier by British and Turkish laboratories.
However, the finding was officially confirmed by the Organisation for the Prohibition of Chemical Weapons (OPCW) on Wednesday (19 April).
The OPCW's Director-General, Ahmet Üzümcü of Turkey, said in a statement: "The results of [our] analyses from four OPCW designated laboratories indicate exposure to sarin or a sarin-like substance.
"While further details of the laboratory analyses will follow, the analytical results already obtained are incontrovertible."
Üzümcü said the finding is based on samples collected from the autopsies of three victims and seven individuals receiving treatment in hospital.
He added that an OPCW fact-finding team was ready to deploy to Khan Sheikhoun independently to ascertain who was responsible.
The US, backed by UK and other allies, said Syrian President Bashar al-Assad was guilty. However, Assad has denied the allegations and, in an interview with AFP, claimed the attack was a "fabrication" to justify the missile strike on Syrian forces.
A similar conclusion to Assad was reached by Theodore Postol, a professor emeritus at the Massachusetts Institute of Technology (MIT), who said images of the sarin canister allegedly used showed inconsistent damage with an aerial explosion.
Safety guarantee needed
However, before the OPCW's fact-finding team can deploy to Khan Sheikhoun and put all speculation to rest, the body needs to be confident in the safety of its experts.
On 27 May, 2014, a joint OPCW-United Nations team investigating an alleged chlorine attack in the province of Hama were attacked by anti-government militants.
According to Reuters reports, a convoy of cars was hit by a roadside bomb, causing the cars to turn back, but only one successfully returned. Two cars with five Syrians and six OPCW team members were captured by militants, but were later released unscathed.
An executive council of the OPCW will meet on Thursday (20 April) to decide whether it can send a team to Khan Sheikhoun.