“Once again the Syrian regime will deny the evidence of its responsibility for this massacre,” Hollande said in a statement.
Earlier, French foreign minister described the attack as “monstrous” and called for an emergency meeting of the UN Security Council.
Ayrault said “chemical weapons” had been used in the attack and that it was “more proof of the savagery that the Syrian people have been subjected to for so many years.”
The attack in the town of Khan Sheikhun left dozens struggling to breathe and displaying symptoms such as foaming at the mouth and vomiting and fainting, the Britain-based Syrian Observatory for Human Rights said.
The European Union too condemned the attack and said that al-Assad bears “primary responsibility” for it.
“Today the news is awful,” EU diplomatic chief Federica Mogherini told mediapersons in Brussels on the sidelines of a EU-UN conference that was meant to focus on the post-conflict situation in Syria.
“But this is a dramatic reminder of the fact that the situation on the ground still continues to be dramatic in many different parts of Syria,” Mogherini said.
“And obviously, there is a primary responsibility there from the regime and first and foremost because it has the primary responsibility of protecting its people and not attacking its people.”
Britain too condemned the attack and called for those responsible to be held to account.
The attack was the latest apparently involving chemical weapons since protests against Assad morphed into a bloody civil war in 2011, which has since left more than 320,000 people dead.
Damascus and the rebels blame each other for the previous chemical attacks, while Washington, London and Paris say Assad is responsible. Moscow, which backs Assad, says there is no clear evidence to back that up.
In 2013 the United States and Russia reached a deal to eliminate Syria’s chemical weapons to avoid US air strikes against the Assad regime after hundreds of people were killed in a sarin gas attack that the US said killed 1,429 people.