Heaps of weapons seized across France in a succession of raids on suspected Islamist militants and total 23 individuals arrested, officials say.
The crackdown follows multiple attacks on restaurants, bars, a concert hall and an arena in Paris on Friday, in which 129 people were killed.
A police operation is also under way in Brussels, Belgium that one suspect was arrested.
Shots and explosions have been heard in the district.
France held a nationwide minute of silence at noon local time (11:00 GMT) for the victims.
French PM Manuel Valls said the strikes were organised from Syria.
He added that the authorities assumed new terror attacks were being planned in France along with other European nations.