Emmanuel Macron has said he has proof the Syrian government used chemical weapons in an air strike on civilians in the city of Douma.
The French president added he would decide on what action to take once all the information had been verified, insisting he would strive to prevent an escalation of conflict across the Middle East.
Mr Macron previously called for a “strong” response to last weekend’s attack on the Syrian town, which left a reported 70 people dead and 500 more injured. The Syrian government denies responsibility.
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His comments came as Chancellor Angela Merkel ruled Germany out of any possible military action in Syria. She added it was hard to do nothing and restated the importance of unity among Western allies.
Donald Trump said on Thursday that a possible military strike against Syria “could be very soon or not so soon at all” while Theresa May is convening a special meeting of her cabinet to discuss a potential military response to the incident.
The French president does not need parliamentary permission to launch a military operation. France is already involved in the US-led coalition to fight Isis in Syria and Iraq.
The attack was first reported by Syrian rebel group Jaish al-Islam on Saturday.
Inspectors with the global chemical weapons watchdog, the Organisation for the Prohibition of Chemical Weapons, are due to investigate the incident.
The UK, US and its allies have promised a joint response to the suspected chemical attack.
Speaking on Wednesday, Ms May said “the chemical weapons attack that took place on Saturday in Douma in Syria was a shocking and barbaric act”, adding that “all the indications are that the Syrian regime was responsible”.
She is not obliged to win parliament’s approval for military intervention, although Jeremy Corbyn has said parliament should be consulted before any action is approved.
Mr Trump has issued a direct threat of a retaliatory strike, saying Russia should “get ready” for missiles to be fired at its ally Syria.