A total of 23 people have been arrested and dozens of weapons seized in a series of raids on suspected Islamist militants across France, officials say.
The crackdown follows multiple attacks on bars, restaurants, a concert hall and a stadium in Paris on Friday, in which 129 people were killed.
Belgian police also carried out raids in Brussels. Shots and explosions were heard in Molenbeek district.
Meanwhile the brother of two suspects, arrested in Belgium, has been freed.
Mohammed Abdeslam’s lawyer said on Monday he had been released without charge, proving his innocence.
His brothers are Brahim Abdeslam, killed during the attacks, and Salah Abdeslam, who is on the run.
Seven people were arrested in Belgium at the weekend and Mohammed Abdeslam is one of five later released.
France held a nationwide minute of silence at midday local time (11:00 GMT) for the victims.
President Francois Hollande led the minute’s silence from the Sorbonne University – an acknowledgement of the young age of so many of the 129 who died, the BBC’s Hugh Schofield reports from Paris.
The country has been slowly, awkwardly getting itself back into some form of routine, but because of the feelings triggered by Friday’s horror, life still does not feel normal, our correspondent adds.