French security services have identified one of the ISIL militants seen in the video showing the beheading of US aid worker Abdul-Rahman Kassig and 18 Syrian soldiers.
They are yet to confirm a second French fighter among the group.
Maxime Hauchard, a Muslim covert from Normandy was already known to intelligence services.
“His case was under investigation and handed over to the Interior Security department even before the publication of this weekend’s video and it’s for the judicial authorities to decide on the outcome using the elements now in the hands of the police,” explained French Interior Minister Bernard Cazeneuve.
Earlier reports that British citizen Nasser Muthana was among the fighters were later denied by his father.
Prime Minister David Cameron elaborated on new powers planned to tackle extremism in the UK announced at the G20 over the weekend.
“As the House knows these include new powers for police at ports to seize passports, to stop suspects from travelling and to stop British nationals returning to the UK unless they do so on our terms.”
Cameron hopes the new anti-terrorism bill will become law by January 2015.
Thousands of Western volunteers have joined ISIL fighters. More than 1,000 French citizens are believed to be involved in jihadi cells in Iraq and Syria.