French Prime Minister Manuel Valls says authorities believe new terror attacks are being planned in France and in other European countries following the carnage in Paris.
"We know that operations were being prepared and are still being prepared, not only against France but other European countries too," he said.
France would be living with the threat of terror attacks "for a long time", he said.
Valls said he was struck by the fact that young people had been targeted in Friday's attacks on a concert hall, bars and restaurants and outside the Stade de France stadium that left 129 people dead.
"Once again the terrorists have attacked France, the French people, young people. Many young people are dead," he said.