The world's leading chemical weapons watchdog, the Organisation for the Prohibition of Chemical Weapons (OPCW) says the banned nerve agent Sarin was used in an attack in Syria in April.
The attack on the town of Khan Shaykhun killed at least 100 people and injured more than 500.
Western intelligence agencies had blamed Bashar al Assad's regime for the attack, but Syrian officials had repeatedly denied using banned toxins in the conflict.
There is "absolutely no doubt" that Assad’s regime was behind the use of chemical weapons in Syria in April, Britain's foreign minister Boris Johnson said on Friday.
Likewise, French foreign ministry said in a statement that the "conclusions of this report are indisputable," and that the organisation's members should act firmly on its findings.
Russia disputed the findings of the OPCW, calling them “largely biased,” TASS news agency quoted Russia's Foreign Ministry as saying.
A UN panel will now try to determine who was responsible.
TRT World met one mother who lost her four children in the attack. Sarah Jones has the story.
Warning: video contains some disturbing footage from the chemical attack.