Speaking to news channel CNEWS, he said: “These crimes must not go unpunished. In any case, there are investigations, United Nations commissions... there will be a war crimes trial.”
At least 86 people were killed on Tuesday in rebel-held Khan Sheikhun in northern Syria in a suspected chemical attack that left people choking and foaming at the mouth.
France is again pushing for a resolution at the United Nations to condemn the attack blamed by the West on Assad's regime, but Ayrault did not sound optimistic after the first discussions on Wednesday at the international body.
“It’s difficult because up to now every time we have presented a resolution, there has been a veto by Russia and sometimes by China ... but we must cooperate because we need to stop this massacre,” he added.
Meanwhile, Turkey said on Thursday the autopsies of three Syrians killed in the attack on Tuesday confirmed that chemical weapons had been used by President Bashar al-Assad's regime.
“Autopsies were carried out on three of the bodies after they were brought from Idlib. The results of the autopsy confirms that chemical weapons were used,” Justice Minister Bekir Bozdag said, quoted by state-run Anadolu news agency.
“This scientific investigation also confirms that Assad used chemical weapons,” Bozdag added, without giving further details.
Thirty-two injured Syrians were brought to southern Turkey for medical treatment but three of them died in hospital.
Autopsies were conducted by officials from the World Health Organization in the southern province of Adana together with officials from Organisation for the Prohibition of Chemical Weapons, Bozdag said.
Turkish President Recep Tayyip Erdogan, a vocal critic of Assad, called the Syrian president a “murderer” on Wednesday after denouncing the world’s “silence” on the deaths.