Western officials believe chlorine was used in the 7 April attack on the main city in the former rebel bastion of Eastern Ghouta.
Dozens of civilians were killed.
They say they have not yet established whether sarin, the agent allegedly used in a chemical attack that prompted US missile strikes last year, was also used.
In an address from the White House on Friday night, US President Donald Trump said precision strikes were carried out on targets associated with the chemical weapons capabilities of the Syrian government.
US Defence Secretary James Matthis said three sites had been targeted well away from any known Russian military bases.
He said that, although Russia had been informed of the strikes, Moscow had not been informed of the exact targets.
British Prime Minister Theresa May gave her support to the joint military action, saying there was no alternative to the use of force in Syria.
French Defence Minister Florence Parly announces participation in air strikes
Cette nuit, sur ordre du Président de la République, les armées françaises, en étroite coordination avec les armées américaines et britanniques, ont mené une opération en Syrie. pic.twitter.com/gAvclwA8r3Florence Parly (@florence_parly) 14 avril 2018
Macron blames Assad government
French President Emmanuel Macron issued a statement saying a red line had been crossed and that France had proof the Syrian regime was responsible for the attack.
France "cannot tolerate the banalisation of the use of chemical weapons", he declared, adding that the attack was "limited to the Syrian regime's capacities that allow the production and the use of chemical weapons".
French Defence Minister Florence Parly said the Western powers targeted "the main research centre" and two production sites of "a clandestine chemical programme" operated by the Syrian government.
"We've hit their capacity to develop, perfect and produce chemical weapons," Parly said.
"The goal is simple: stop the regime from using chemical weapons again."
French warships used
France provided warships in the Mediterranean Sea as well as sending in fighter jets stationed at bases in France.
"These carried out coordinated cruise missile strikes ... in tight coordination with our American and British allies," Parly said.
France wants to start working "right now" on resuming the political process aimed at ending the conflict in Syria, Le Drian said Saturday.
"A plan for ending the crisis must be found, with a political solution. We are ready to start working right now with all countries who want to participate," he said.
Russia warns of 'consequences'
The Russian defence ministry reported that none of the Western strikes in Syria had hit areas near Russia's air and naval bases.
It said over 100 missiles had been fired at Syria and a significant number intercepted by Syrian defence forces, but without giving figures.
Moscow's ambassador to the United States, Anatoly Antonov warned that such actions would not be without consequences.
Russia has suggested the strikes were coordinated to block a fact-finding mission organised by the Organisation for the Prohibition of Chemical Weapons, which is on its way to Syria and due to begin its probe, following an invitation from Damascus.
Meanwhile UN Secretary-General Antonio Guterres warned against a "full-blown military escalation" in Syria.
Since last weekend, there has been a sustained military buildup in the eastern Mediterranean.
A French frigate, British Royal Navy submarines and an American destroyer, have all moved into range of Syria's coast.