France's foreign ministry says deadly sarin gas used in a chemical attack in Syria this month that killed 87 people "bears the signature" of President Bashar Assad's government.
A six-page report by French intelligence services claims the nerve agent came from hidden stockpiles of chemical weapons that Damascus was supposed to have destroyed under an U.S.- and Russian-brokered deal in 2013.
The chemicals in the gas matched those from samples taken following a sarin attack in Syria in 2013 carried out by government helicopters.
"There's no doubt that sarin was used. Now there's no longer any doubt that the Syrian regime was responsible," Jean-Marc Ayrault, the French foreign minister, said after presenting the report to the defense council at the Elysee Palace on Wednesday.
Syria has repeatedly denied being responsible for the April 4 attack on Khan Sheikhoun, in Idlib province in the northwest of the country, arguing either that it never happened or that it was carried out by rebels. Moscow, which supports Assad, dismissed the French report, saying there was no proof the Syrian government was responsible.
The French investigation concluded that the chemical weapon used had been delivered by air; only Assad's forces have planes and helicopters.
Ayrault insisted that France knows from "a certain source … that the manufacturing process of the sarin that was sampled is typical of the method developed in Syrian laboratories."
"This method is the signature of the regime, and it is what enables us to establish responsibility for the attack. We know because we kept samples from previous attacks that we were able to use for comparison," Ayrault said.
French intelligence operatives made the link from blood taken from the attack victims in a hospital and examined by the National Center for Scientific Research.
Laboratory tests revealed the presence of a "signature" characteristic in the gas, the presence of hexamine, that pointed to its being manufactured by the Syrian government. It matched the sarin in a 2013 chemical bomb dropped by a helicopter on the town of Saraqeb, in the northwest of the country, which failed to explode.
"These attacks by the Syrian regime should be seen in the context of the continuous use of weapons or chemical agents, mostly in air attacks, since 2013. … France has been able to confirm on several occasions the use of chlorine and sarin," the French intelligence report says.
"Based on this overall evaluation and on reliable and consistent intelligence collected by our services, France assesses that the Syrian armed forces and security services perpetrated a chemical attack using sarin against civilians in Khan Sheikhoun on 4 April, 2017," the report concludes.
The U.S., Britain and Turkey already had collected their own evidence and concluded that sarin was used in the attack, which was condemned internationally and prompted a U.S. missile strike on a Syrian air base.
Last week, the Organization for the Prohibition of Chemical Weapons declared that "incontrovertible" test results showed sarin or a chemically similar substance was used in the April 4 attack.
Ahmet Uzumcu, the group's director-general, said in a statement that analysis at four laboratories of the bodies of three victims and seven survivors suggested exposure to "sarin or a sarin-like substance."
The nerve agent sarin attacks the body's central nervous system, causing breathing difficulties and death. It is banned under international law.
France's Foreign Ministry said it remained "committed to ensuring that the perpetrators of this heinous attack are held accountable."
Willsher is a special correspondent.
9:45 a.m.: This article was updated throughout with staff reporting.