The Syrian government is responsible for the April chemical attack in Khan Sheikhoun town in which over 80 people were killed, according to the findings of an investigation mandated by the UN Security Council.
"The Islamic State used sulfur mustard in a September 2016 attack in Umm Hawsh and the Syrian government was responsible for the release of sarin in an April 2017 attack in Khan Sheikhoun in Syria," said Edmond Mulet, head of the Joint Investigative Mechanism (JIM) of the Organization for the Prohibition of Chemical Weapons and the UN.
"There has been sufficient evidence of a credible and reliable nature to make its findings," Mulet told the Security Council on Tuesday.
He said that despite the challenges of investigating complex cases during an armed conflict, JIM has taken great care to ensure that its methodology and findings were technically and scientifically sound, Xinhua news agency reported.
Although it was too "dangerous" to visit Umm Hawsh and Khan Sheikhoun, the panel considered that sufficient information had been gathered to come to a solid conclusion.
On April 4, more than 80 people were killed in a suspected chemical attack in Khan Sheikhoun in Syria's Idlib province, a rebel-held area in north-western Syria.
Syrian President Bashar al-Assad repeatedly stressed that the alleged chemical attack was "fabricated".
"There was no toxic attack in Khan Sheikhoun town," Assad had said, charging that the US and the Western powers prevented an investigation team from coming into Syria to look into the allegation, "because the team will find that all the narrative about what happened in Khan Sheikhoun was mere lies".
The Syrian Foreign Ministry said "the Syrian Army doesn't possess chemical weapons and hasn't used them before in any Syrian city".
Two women were injured in the Umm Hawsh incident, a mustard gas attack, on September 16, 2016.