A previous investigation by chemical weapons inspectors had identified the use of sarin at Khan Sheikhoun but did not say who was responsible.
In the most conclusive findings to date from investigations into chemical weapons attacks during the conflict, the UN Commission of Inquiry on Syria said a regime warplane dropped sarin on Khan Sheikhoun in Idlib province in April, killing more than 80 civilians and injuring nearly 300.
Twenty-seven were by President Bashar al-Assad's forces, including seven between March 1 to July 7. Investigators have so far been able to pinpoint who was responsible for the six remaining attacks which all occurred earlier in the conflict.
US President Donald Trump cited images of the aftermath of the Khan Sheikhoun attack when he launched a punitive strike days later, firing cruise missiles on a Syrian government-controlled air base, from where US officials said the Syrian military had launched the chemical attack.More news: All Myanmar Muslims suffering state-backed persecution: Rights group
A government warplane dropped sarin on the town in Idlib province, killing more than 80 civilians, the UN Commission of Inquiry on Syria said, in the most conclusive findings to date from investigations into that chemical weapon attack.
After the chemical attack on Khan Sheikhoun, the United States launched missiles from the Mediterranean at an airbase east of Homs in central Syria, from which the aircraft that dropped the bombs with sarin most likely took off.
- Investigators believe chemical weapons including Sarin were used around 27 times.
United Nations rights investigators have concluded that Syria's air force carried out a deadly nerve gas attack in April that drew global condemnation, while Russian strikes helped to destroy hospitals that could have treated victims.More news: Congressional Democrats back Harvey aid with three-month debt limit increase
The report also highlighted civilian deaths caused by US coalition strikes in its fight against the self-proclaimed Islamic State (ISIS), including the series of strikes on a prayer hall next to a mosque in Aleppo, which resulted in dozens of civilian deaths, including children, on March 16.
It was "extremely unlikely that an air strike would release sarin potentially stored inside such a structure in amounts sufficient to explain the number of casualties recorded", the report said.
At least 83 people were killed during the attack.
Investigators were not granted access to Syria and based their report on photos of bomb remnants, satellite imagery and witness accounts.More news: IFA 2017: Huawei reveals low-power Kirin 970 mobile AI chipset
The report, which also documents violations by al-Qaida's branch and other militant groups in Syria, comes at a time of considerable change in the political and diplomatic landscape and the emergence of de-escalation zones that have sharply reduced fighting in some areas. A US-led coalition is also battling the extremist group in Syria. It said that the attack amounted to a war crime.
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