France will launch strikes if proof emerges that the Syrian regime has used banned chemical weapons against its civilians, President Emmanuel Macron has said.
"We will strike the place where these launches are made or where they are organised," Mr Macron said.
"But today our services have not established proof that proscribed chemical weapons have been used against civilian populations."
"As soon as such proof is established, I will do what I said," Mr Macron warned, while adding that "the priority is the fight against the terrorists, the jihadists".
Regarding the Syrian regime itself, either during or after the conflict, he said: "It will be answerable to international justice."
Mr Macron also called for an international meeting on Syria, in the region if possible.
In a telephone call with Russian President Vladimir Putin on Friday, Mr Macron said he was "worried about indications suggesting the possible use of chlorine on several occasions against the civilian population in Syria these last few weeks".
Russia has intervened alongside Syrian regime forces in the seven-year civil war and Mr Putin is seen as the foreign leader with the most influence over Syrian President Bashar al-Assad.
Receiving Mr Putin at Versailles in May 2017, Mr Macron had declared that France would respond immediately to any use of chemical weapons in Syria.
"A very clear red line exists on our side: the use of chemical weapons by anyone," Mr Macron said, promising "retaliation and an immediate response from France".
According to the US, at least six chlorine attacks have been reported since early January in rebel areas, with dozens injured.
The Syrian government in late January denied carrying out chemical weapons attacks and its ally Russia denounced the charges as a "propaganda campaign", stressing that the perpetrators had not been identified.
While France, like the United States, suspects the Syrian regime, it says it does not yet have concrete evidence on the nature and origin of the attacks.
Syria has repeatedly been accused of using chemical weapons, with the United Nations among those blaming government forces for an April 2017 sarin gas attack on the opposition-held village of Khan Sheikhun that left scores dead.