The world chemical weapons control body says it is very likely that nerve agent Sarin and chlorine have been used in attacks against a Syrian village last year.
The Organization for the Prohibition of Chemical Weapons concluded that Sarin was used as a weapon in the south of Latamina, controlled by the rebels, on March 24, 2017, and the chlorine in his hospital the following day.
He did not attribute the blame for the incidents, in accordance with his mandate.
But activists said at the time that the area was under attack by government forces.
The government has repeatedly denied the use of chemical weapons.
However, a joint UN-OPCW mission that ended recently said it was confident that government forces used Sarin in an attack on the rebels. He held the city of Khan Sheikhoun only a few days after the incidents in nearby Latamina.
The statement issued by the OPCW Mission of Inquiry (FFM) said that its conclusions on the possible use of Sarin and chlorine in Latamine were based on testi analysis of epidemiology and environmental samples.
He did not provide any details about what happened in the incidents, but a commission of inquiry from the UN Human Rights Council reported on the events of March 25.
It said a Syrian air A force helicopter threw a day on what was believed to have been a barrel bomb full of chlorine in Latamina hospital and killed three civilian men: a surgeon and two patients.
Witnesses told investigators that the bomb made a slight noise before emitting a yellow-green smoke that smelled strongly of cleaning agents.
At least 32 people were injured as a result of the attack. Most of them suffered from throat and eye irritation, shortness of breath, vomiting and foam from the mouth.
The commission of inquiry quoted the director of the OPCW as saying that Sarin was released in another attack on Latamina on March 30, 2017. At least 85 people suffered breathing difficulties after an unidentified fighter aircraft dropped an bomb in the village that day, he said.
OPCW is also investigating an alleged chemical attack in April 2018 in the city of Douma, then controlled by the rebels, in which doctors say 40 people were killed.
The United States, the United Kingdom and France said they were confident that government forces had used weapons in Douma and, in response, had conducted missile attacks against Syria's "chemical weapons infrastructure".
In a recent interview with the Daily Mail, Syrian President Bashar al-Assad insisted that the three Western countries had "staged" the incident in Douma, which took place shortly before the city fell to government forces.
"It was a lie, after we released that area, our information confirmed that the attack did not take place," he said. "The British government should prove with evidence that the attack happened, and then they should prove who is responsible."