The attack on the town of Douma on 7 April killed dozens of people, including children.
French and U.S. officials were "working very closely, and we will have decisions to take, at the time we choose, when we consider it most useful and most effective".
Asked if he has been in touch with President Donald Trump regarding a possible military intervention, Macron said that he speaks daily with his American counterpart.
Sir John Sawyers, the former head of MI6, called for a much more punitive and targeted attack on Syria than the operation authorised by Mr Trump previous year against a Syrian airbase.
It comes as the British Prime Minister Theresa May holds a special "war cabinet" to discuss her options.More news: Victory by Viktor Orban rings alarm bells in other European Union capitals
Damascus has also pointed to reports from the Red Crescent, which confirmed it hadn't received any reports of such an incident and the Russian Reconciliation Center in Syria, which sent specialists to ground immediately after the alleged chemical attack.
French President Emmanuel Macron said on Thursday he has proof that the Bashar al-Assad regime in Syria had used chemical weapons in the attack in suburban Damascus on Saturday. Dmitry Peskov added that it would have an "utterly destructive impact on the Syrian settlement". "What is different this time is the fact that the escalation has now happened". The former Conservative deputy leader Kenneth Clarke called on Mrs May to rethink her stance.
Asked if and when Syrian facilities would be targeted, Macron replied: "When we decide, and we will have to verify all the information". You don't just waive aside accountability to parliament because it is inconvenient.
Syria and its ally Russian Federation have both denied involvement amid worldwide outrage over Saturday's incident.
The global chemical weapons watchdog said it will go to Douma "shortly", but it's unclear how much evidence might remain.More news: Everyone is saying the same thing after Joe Hart's performance against Chelsea
The World Health Organization (WHO) has said 500 patients were treated for symptoms of exposure to toxic chemicals.
Government ministers in Britain agreed at an emergency meeting in London on the need for a response to the chemical weapons attack. On April 10, French Prime Minister Edouard Philippe had called for a resolute reaction from the worldwide community to the attack.
Chancellor Angela Merkel says Germany won't participate in possible military action in Syria, but supports sending a message that the use of chemical weapons is unacceptable.
"Of course, the chemical attack is what pushed us to agree" to a withdrawal from Douma, said high-ranking Jaish al-Islam member Yasser Dalwan.More news: Pat Shurmur: Odell Beckham on hand, "wants to be great"