"For months I have said it is necessary to cooperate with Russia, Iran and Bashar Assad's regime to combat the Islamic State. We have lost plenty of time," Fillon said.
Earlier, he expressed regret about the fact that France has no military strategy to fight Islamic State militants. He stressed that France's main mistake was its reluctance to clinch an alliance with Russia.
The Islamic State currently remains a major threat to global security.
According to various estimates, ISIL's self-proclaimed caliphate currently spreads across 90,000 square kilometers, making the size of the terrorist-controlled territory slightly bigger than the Republic of Ireland.
Some claim that there are around 50,000 Islamic State militants, while others put the figure at a whopping 200,000.