Speaking at the Elysee Palace in Paris, France's Foreign Minister Jean-Yves Le Drian said the country had "acted in accordance with our words, in accordance with our responsibility and in coordination with our allies."
"The regime of Mr Assad deliberately decided to break the taboo of the 20th century, which is the use of chemical weapons," Le Drian said in a statement on behalf of French President Emmanuel Macron.
"(Assad) hasn't hesitated to break international law."
He added France had three imperatives going forward: The dismantling of the Syrian chemical weapons program, a ceasefire across Syria, and a crisis exit plan.
At 3 a.m. Paris time, French forces "in close coordination with US and British troops" conducted an operation in Syria, said French Defense Minister Florence Parly.
"On a practical level, this operation required air and naval means, multi-mission frigates accompanied by support ships were deployed in the Mediterranean Sea. At the same time an air raid left at night from multiple air bases in France," she said.
"These different means fired... cruise missiles at the chosen targets in close coordination with our British and American partners."
She added that France does "not seek confrontation, and we refuse any possibility of military escalation."
"We had ensured that the Russians were warned beforehand," Parly said.