French Prime Minister Manuel Valls said 49 French citizens have been killed in Syria, fighting alongside jihadists.
Mr Valls said the French government was aware of more than 1,000 French nationals who are involved in "this phenomenon."
Speaking following a security meeting in Beauvais, north of Paris, the prime minister said "....we are not surprised to learn that French citizens or residents of France are found at the heart of these cells and taking part in this barbarity."
"This strengthens our determination to fight against terrorism," he added.
Two 22-year-old French citizens, Maxime Hauchard and Michael Dos Santos, have been identified as appearing in this weekend's execution video from the self-proclaimed Islamic State group.
Meanwhile, France will deploy six Mirage fighter jets to Jordan as it steps up attacks against the Islamic State group in Iraq, defence minister Jean-Yves Le Drian announced today.
"French air forces will be reinforced with six Mirages to be stationed in Jordan," Mr Le Drian said, speaking in parliament.
