The international chemical weapons watchdog says chlorine was likely used as a weapon in the Syrian town of Saraqeb in early February, the latest report of poison gas being unleashed in Syria's civil war.
The Organisation for the Prohibition of Chemical Weapons on Wednesday released details of a report into the chlorine use, but did not say which side in the fighting used it. The OPCW is not mandated to apportion blame for the attack.
The OPCW said that its Fact-Finding Mission probing alleged use of chemical weapons in Syria "determined that chlorine was released from cylinders by mechanical impact in the Al Talil neighbourhood of Saraqeb."
On February 4, the White Helmets search-and-rescue group and a medical charity reported that several people suffered breathing difficulties after a suspected chlorine gas attack on Saraqeb, days after the Trump administration accused President Bashar Assad's government of producing and using "new kinds of weapons" to deliver poisonous gases.
Damascus denied the White House's charges.
The White Helmets said three of its rescuers and six other people suffered breathing problems. The Syrian American Medical Society said its hospitals in Idlib treated 11 patients for suspected chlorine gas poisoning.
OPCW Director-General Ahmet Uzumcu harshly criticised the chemical attack.
"I strongly condemn the continued use of toxic chemicals as weapons by anyone, for any reason, and in any circumstances," Uzumcu said in a statement. "Such acts contradict the unequivocal prohibition against chemical weapons enshrined in the Chemical Weapons Convention."
The OPCW said its team based its findings on evidence including "the presence of two cylinders, which were determined as previously containing chlorine; witness testimony; environmental samples that demonstrated the unusual presence of chlorine in the local environment; and the number of patients at medical facilities shortly after the incident who showed signs and symptoms consistent with exposure to chlorine and other toxic chemicals."
The mission also is investigating allegations that poison gas was used in Douma, near the capital Damascus, in a deadly April 7 attack.
That attack led to the US, France and Britain blaming the Syrian government and launching joint punitive air strikes targeting suspected Syrian chemical weapons facilities on April 14. The organisation has not yet issued a report on that attack.
Assad's forces have repeatedly been accused of using chemical weapons in the civil war. His regime denies the allegations. Rebels also have been accused of using poison gas.