France says Assad's allies enabling him to act with impunity in Syria

"Once again the Syrian regime will deny the evidence of its responsibility in this massacre. Like in 2013, Bashar al-Assad counts on the complicity of his allies to act with impunity," Hollande said in a statement on Tuesday.

A suspected Syrian government chemical attack killed at least 58 people, including 11 children, in the northwestern province of Idlib earlier on Tuesday, a monitor, medics and rescue workers in the rebel-held area said.

"Those who support this regime can once again assess the magnitude of their political, strategic and moral responsibility," he said.