French fighters make up the largest contingent of Europeans being recruited to join Muslim extremists in Iraq and Syria, and security officials fear they will return newly skilled in warfare and carry out attacks at home.
Calls by the Islamic State group for lone-wolf attacks in the West have heightened anxiety. A Frenchman who is believed to have fought with the organisation is charged in a deadly shooting at a Brussels Jewish museum.
He gave no details on the five attacks he said had been stopped since August 2013, beyond saying they were planned either by recent returnees from Syria or those who had not yet left for the war zone.
Two young women accompanied by two children were blocked at the Paris airport on Saturday en route to Turkey, Cazeneuve said in a report to the government. But many leave unimpeded, especially young people who hide their intentions to family and friends.