Syrian President Bashar Al Assad's air force attacked a rebel town with sarin and chlorine in 2017, the world's chemical weapons watchdog said in its most direct report against the regime.
The Organisation for the Prohibition of Chemical Weapons, or OPCW, said that on three occasions, between March 24 and 30 in 2017, the air force dropped sarin and chlorine on Ltamenah in Hama province, affecting at least 106 people.
The town later fell to the regime.
Santiago Onate-Laborde, co-ordinator of the watchdog's investigation and identification team, said the attacks "would have only taken place on the basis of orders from the higher authorities" of Syria's military command.
The first and last attacks were carried out by a Sukhoi Su-22 plane from the 50th Brigade of the 22nd Air Force Division.
Both times the plane dropped two M4000 bombs containing the nerve agent sarin on southern Ltamenah, the agency's report said.
On March 25, 2017 a regime helicopter dropped a cylinder on the Ltamenah hospital, which "broke in through its roof, ruptured and released chlorine", the report said.
The Syria Campaign, a grassroots group campaigning for a democratic Syria, said the report comprised "independent, irrefutable proof that Assad gassed civilians".
"The next step must of course be justice for all those who were killed by the Syrian regime," the Syria Campaign said.
Almost two years ago, the organisation confirmed that sarin and chlorine were used in two attacks in Ltamenah.
At the time it did not name those responsible but the UN asked it in 2018 to "put in place arrangements to identify the perpetrators of the use of chemical weapons" in Syria.
Another deadly sarin assault took place on April 4, 2018, in Khan Sheikhoun, in Idlib province. It killed more than 80 people.
Khan Sheikhoun was a centre of non-violent resistance against Mr Al Assad’s rule before the Syrian uprising turned into an armed rebellion in 2012.
The first large-scale use of chemical weapons in the civil war was in the rebel region of Eastern Ghouta near Damascus.
It led to US threats of striking Mr Al Assad's forces and an eventual deal to strip the regime of its chemical weapons.
Washington said up to 1,800 civilians were killed in the Eastern Ghouta attack.
Victims of the attacks in Syria since 2013 have been overwhelmingly among the country's majority Sunni population.
The regime's military and the ruling elite are dominated by members of the Alawite sect, to which Mr Al Assad belongs.
The watchdog's head, Fernando Arias, said it was not a "judicial or quasi-judicial body with the authority to assign individual criminal responsibility."
"It is now up to the Executive Council and the Conference of the States Parties to the Chemical Weapons Convention, the United Nations Secretary-General, and the international community as a whole to take any further action they deem appropriate and necessary,” he said.