SYRIA OPPOSES: President Bashar al-Assad's office denounced the USA strike as 'reckless, irresponsible behavior'.
German Chancellor Angela Merkel discussed the attack with Macron on Thursday, her office said.
Macron did not describe the evidence or say how France got it.
Mr Macron said he has been talking regularly this week with US President Donald Trump about the most effective response.
"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.
While the Commission "reiterates the need for accountability in Syria for all war crimes committed, in particular the use of chemical weapons", its spokeswoman refused to comment on whether Brussels would support military action.
But he repeated that he wanted to also avoid "an escalation".
He did not say whether France is planning military action against Assad's government.
The regime in Syria and its ally Russian Federation have vehemently denied that the Assad regime is behind the attack, instead pinning it on rebels. Trump tweeted Thursday: "Never said when an attack on Syria would take place".
Merkel, who spoke with Macron by telephone, told him that she was concerned that the worldwide community's ability to enforce a ban on the use of chemical weapons was eroding. He spoke during a meeting with Ali Akbar Velayati, an aide to the supreme leader of his ally, Iran.
Assad says the Western threats endanger worldwide peace and security, and that military action would only contribute to the "further destabilization" of the region.
There was no immediate confirmation or indication from Assad's government that Syrian troops entered Douma on Thursday. Syrian activists and rescuers say the attack on Douma killed more than 40 people, allegations denied by the government.
There was no official announcement by Damascus that its forces had retaken the town of Douma, located near the capital Damascus, from rebels.