And he called on Assad's main ally, Russia, which condemned the bombings, to persuade him to talk peace.
"It is to be hoped now that Russia will understand that, after the military response to the Syrian arsenal, we must combine our efforts to promote a political process that will allow an end to the crisis in Syria," he said.
Assad is the obstacle to that process, Le Drian went on. "It's up to Russia to put pressure on him."
Saying that he would raise the Syrian crisis at a European Union foreign affairs ministers meeting on Monday, Le Drian also took aim at Assad's other ally, Iran, declaring that "everything possible must be done to avoid Iran's military presence in Syria does not lead to a conflict outside Syria's borders".
President Donald Trump has toughened the US's stance on the Islamic republic, which is the bête noire of both Israel and Saudi Arabia.
French President Emmanuel Macron said he hoped to work with Turkey to "combat impunity iwith respect to chemical weapons and allow the establishment of an impartial and solid mechanism at the United Nations" in a phone call to Turkey's Recep Tayyip Erdogan on Saturday.
Although Macron has criticised the Turkish offensive against Kurdish militias in Afrin, he thanked Erdogan for his support for the airstrikes.
The French parliament will debate the air strikes on Monday but there will be no vote.
Some politicians, notably left-winger Jean-Luc Mélenchon, have complained that parliament was not consulted on the air strikes.
UN draft resolution
France has now joined the US and the UK in taking the battle to the UN.
A Russian effort to persuade the Security Council to condemn the air strikes failed on Saturday.
The three countries are now circulating a draft resolution calling for an investigation into chemical weapons attacks in Syria.
It also calls for unimpeded deliveries of humanitarian aid, the enforcement of a ceasefire and Syrian government engagement in UN-led peace talks.
Negotiations on the draft are due to begin on Monday but diplomats say it is unclear when it will be voted on.
Western diplomats said they were ready to allow time for negotiations to make every effort to bring Russia aboard.
Russia has used its veto 12 times at the Security Council to block action targeting its Syrian ally.
Inspectors from the Organisation for the Prohibition of Chemical Weapons arrived in Syria to verify claims that chemical weapons were used in the 7 April attack in Eastern Ghouta.
German Foreign Affairs Minister Heiko Maas this weekend said that his country will join France in creating an international grouping of "influential countries" to revive the political process.