France has said it will provide proof within days that Syrian president Bashar Assad's regime carried out the April 4 chemical attack in Syria which killed at least 90 people.
Foreign minister Jean-Marc Ayrault said: "We will provide proof that the regime did indeed organise these strikes with chemical weapons."
He said he could not provide evidence now because analysis is still under way, but added: "In a few days I'll be able to provide proof."
Mr Assad has denied that he was behind the attack. Syria agreed to give up its chemical weapons arsenal in 2013.
French presidential candidate Jean-Luc Melenchon called on the United Nations to punish those behind the attack and said "whoever uses chemical weapons should be condemned".