The Syrian government has denied the allegations and called the reports fake news that the West uses to justify attacking the country.
The Russian government has indicated that it would react if its forces felt threatened by a possible western strike against the Assad regime.
However, he added, France could not give "regimes who think they can do anything" free rein to violate worldwide laws and the global ban on the use of chemical weapons.
The French president, who said he was in daily contact with President Trump, said any strikes would go after Syria's "chemical capabilities".
He said if there were strikes they would not target the Syrian government's allies or anybody in particular, but would be aimed at the Syrian government's chemical facilities.
Also on Thursday, US Secretary of Defense Jim Mattis told a congressional panel: "I believe there was a chemical attack and we are looking for the actual evidence".
"We have proof that chemical weapons, at least chlorine, were used, and that they were used by the Bashar al-Assad regime", the French president said in an hour-long midday TV interview.
Taliban Kill a Governor and Overrun a Government Compound
The center of Khwaja Omari district is 10kms far from Ghazni City and shares a border with Jaghato district of Wardak province. Rahmani said the Taliban planted mines to stop reinforcements from coming to help the government forces fend off the attack.
She said she spoke on Thursday with Mr Macron.
Assad said that there had been no chemical weapons attack in Idlib, and that the opposition reports were a false flag operation and a fabrication aimed at justifying the U.S. missile strike against the Syrian government airbase.
With increasing concerns about a US-Russia proxy war in Syria, Mr Macron insisted that "France will not allow an escalation or something that could damage the stability" of the region.
Kremlin spokesman Dmitry Peskov cautioned against "any steps which could lead to an escalation of tensions".
It "could be very soon or not so soon at all", tweeted the president, who has cancelled a planned trip to allow him to stay in the United States with his defence secretary, and has been canvassing support for strikes from the leaders of France and the UK.
That attack in Duma, a rebel-held town in Syria's eastern Ghouta region, left dozens dead, including children.
Douma was the last major rebel stronghold near Damascus.