John Bacon

USA TODAY

French intelligence services will soon provide proof that Syrian President Bashar Assad's military used chemical weapons in an attack this month that killed scores of civilians, most of them women and children, Foreign Minister Jean-Marc Ayrault said Wednesday.

Ayrault made his assertions on French TV the same day an international investigative group confirmed the victims were exposed to sarin or a sarin-like substance. Sarin disrupts the nervous system, and one drop can be fatal. The gas, like all chemical weapons, is banned under international law.

"As far as French intelligence services and military intelligence are concerned, in a matter of days we will prove that the regime has indeed organized these strikes with chemical weapons," Ayrault said.

The attack April 4 on the town of Khan Sheikhoun killed more than 90 people and left hundreds more suffering from effects of the gas. Images of the tiny victims sparked global outrage against Assad. The U.S. responded by firing 59 Tomahawk cruise missiles at the air base where the Syrian attack originated.

Russia and Syria have claimed conventional Syrian weaponry struck a rebel chemical weapons depot, causing the tragedy.

A similar global outcry after a sarin attack in 2013 resulted in a U.S. and Russian program to destroy Syria’s chemical weapons stockpile. However, chemical weapons attacks in 2014 and 2015 have been verified by the U.N.

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On Wednesday, the Organization for the Prohibition of Chemical Weapons announced that bio-medical samples collected from three victims during their autopsies indicated they were exposed to sarin or a sarin-like substance. Tests on seven people undergoing treatment at hospitals indicated the same thing, said Ahmet Uzumcu, the agency's director-general.

Uzmucu called the evidence "incontrovertible" and said the investigation was continuing.

Also Wednesday, multiple Israeli defense officials told the Associated Press that Assad still has up to three tons of chemical weapons. A senior military official told AP Israeli military intelligence estimates that Assad has “between one and three tons” of chemical weapons. AP said the officials spoke on condition of anonymity under military briefing rules. The assessment was confirmed by two other defense officials, AP said. The Jerusalem Post published a similar report.

The Post, citing a defense official, also said the regime used the chemical weapons out of frustration after failing to make meaningful advances on the ground despite support from Russia, Iran and Hezbollah.