Islamic State group fighters could flee to Egypt or Tunisia after being flushed from their former Libyan stronghold of Sirte, French Defence Minister Jean-Yves Le Drian warned Monday.

"We should begin to look seriously at the question of the spread of the terrorists once Sirte... (is) emptied of the terrorists," Le Drian told a defence conference in Paris.

"They don't disappear. There's a new risk that appears," he said, adding: "Indirectly this will pose new risks for Tunisia and Egypt."

He said it was a "shame, perhaps political reasons prevent it, that all the neighbouring states of Libya don't meet" over the issue.

Backed by weeks of US air strikes, forces loyal to Libya's Government of National Accord (GNA) have recaptured nearly all of what had been the Islamist militants' main stronghold in North Africa.

Pro-GNA forces launched a new attack on Saturday against IS group in Sirte, saying Sunday it could take several days to gain full control of the city.