An investigation by the international chemical weapons watchdog confirmed Friday that sarin nerve gas was used in a deadly April 4 attack on a Syrian town, the latest confirmation of chemical weapons use in Syria's civil war.

The attack on Khan Sheikhoun in Syria's Idlib province left more than 90 people dead, including women and children, and sparked outrage around the world as photos and video of the aftermath, including quivering children dying on camera, were widely broadcast.

"I strongly condemn this atrocity, which wholly contradicts the norms enshrined in the Chemical Weapons Convention," Organisation for the Prohibition of Chemical Weapons Director-General Ahmet Uzumcu said in a statement. "The perpetrators of this horrific attack must be held accountable for their crimes."

The investigation did not apportion blame. Its findings will be used by a joint United Nations-OPCW investigation team to assess who was responsible.

The US State Department said in a statement issued after the report was circulated to OPCW member states that "the facts reflect a despicable and highly dangerous record of chemical weapons use by the Assad regime."

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 U.S. officials said the Syrian military had launched the chemical attack.

It was the first direct American assault on the Syrian government and Trump's most dramatic military order since becoming president months before.

Syrian President Bashar al-Assad has denied using chemical weapons. His staunch ally, Russian President Vladimir Putin, said earlier this month that he believed the attack was "a provocation" staged "by people who wanted to blame him (Assad) for that."

Both the US and the OPCW were at pains to defend the probe's methodology. Investigators did not visit the scene of the attack, deeming it too dangerous, but analyzed samples from victims and survivors as well as interviewing witnesses.

Syrians make fuel from plastic waste Show all 8 1 /8 Syrians make fuel from plastic waste Syrians make fuel from plastic waste Sifting through plastic: the workshop uses plastic from bottles and other waste materials to produce liquid and gas fuels. The liquid is refined into gasoline, diesel and benzene fuels, which in turn are sold for domestic and commercial use Reuters Syrians make fuel from plastic waste Khodor, 20, at the workshop in the rebel-held and besieged neighbourhood of Douma, Damascus Reuters Syrians make fuel from plastic waste Back to basics: a man checks the heat of a pipe pouring with fuel Reuters Syrians make fuel from plastic waste Khodor, 20, must keep an eye on the burning plastic inside the workshop in Douma Reuters Syrians make fuel from plastic waste A young man takes a container of the locally made fuel, which can be used for domestic heating and on farms and bakeries Reuters Syrians make fuel from plastic waste Abu Fahad on a rest break with his colleagues inside the workshop, where the air is heavy with toxic fumes Reuters Syrians make fuel from plastic waste Fuel drips into a container at the workshop. Most locals are glad of the family-run business, which has restored a degree of normality to the region Reuters Syrians make fuel from plastic waste Khodor extracts fuel from plastic in the workshop Reuters

"A rigorous methodology was employed for conducting an investigation of alleged use of chemical weapons that took into account corroboration between interviewee testimonies; open-source research, documents, and other records; and the characteristics of the samples including those provided by the Government of the Syrian Arab Republic," the OPCW said in a statement.

The Syrian government joined the OPCW in 2013 after it was blamed for a deadly poison gas attack in a Damascus suburb. As it joined, Assad's government declared some 1,300 tons of chemical weapons and precursor chemicals which were subsequently destroyed in an unprecedented international operation.