Macron, who tweeted a picture of himself in a meeting room with military and diplomatic advisers, said a debate about France's military involvement would take place in parliament.
Macron's tough statement also contrasted with remarks by major European partners. Meanwhile, Britain has stressed the need for global chemical-detection teams to visit the site of Saturday's attack, the former rebel stronghold of Douma east of Damascus. It also said Syrian air defenses had responded to the US-British-French attack.
"I can not tell you that we have evidence, although we certainly have a lot of media or social media indicators that either chlorine or sarin were used", he told the House Armed Services Committee on Thursday.
But the global body charged with independently verifying the deadly attack, the Organization for the Prohibition of Chemical Weapons (OPCW), has not been given access to the site of the alleged chemical attack in Douma.
She said she spoke on Thursday with Mr Macron.
Now, Trump claims he never wrote when. "Could be very soon or not so soon at all!"
French President Emmanuel Macron said his "red line" had been crossed by the Syrian regime as he launched airstrikes on the country alongside the U.S. and United Kingdom today.
Opinion polls suggested that the British public's support for strikes was lukewarm.
In the years since, the public has questioned the intervention, which became a regular talking point for Sarkozy's critics, including Macron.
The sources said if France were to attack, the strikes would most likely come from warplanes rather than its naval frigate off the Lebanese coast, and that they would likely to take off from France rather than its Middle East bases.
He added that the facts and the responsibility of the Syrian regime were beyond doubt.
"This action was proportionate and targeted, it was not aimed at (Syrian President Bashar al) Assad's allies nor at the civilian population", Foreign minister Jean-Yves Le Drian told journalists.
Moscow, which offers military support to the Syrian regime, has warned of a possible Russian response to a USA attack. France is already involved in the US-led coalition to fight Isis in Syria and Iraq.
'The red line set by France in May 2017 has been crossed, ' he said.