In order to fight IS, "there must be two measures: bombings... and ground troops who cannot be ours, but who should be of the (opposition) Free Syrian Army, Sunni Arab forces, and why not regime forces too," Fabius said in an interview with RTL radio.
But he told AFP shortly afterwards he meant that regime forces could take part "within the context of a political transition -- and only in this context".
The principal target of military efforts remains Raqa, the Syrian city that is the stronghold of IS, Fabius said. Russian and French jets have targeted the town in recent days.
"For us it is one of the main military targets, even the main one, because it is the nerve centre of Daesh, and the attacks against France were planned from there," Fabius said, using another name for IS.
French President Francois Hollande said after talks with President Vladimir Putin in Moscow on Thursday that Syrian President Bashar al-Assad, who is strongly backed by Russia, "has no place in the future of Syria."
However, France and some other Western nations have lately softened their approach to Assad, suggesting he could be part of a transitional process to end a war that has left 250,000 people dead.