Some 500 extra troops are being deployed around Paris after three days of terror in the French capital killed 17 people.
Interior Minister Bernard Cazeneuve said all necessary measures were being taken to protect the country.
Police in France are hunting for any accomplices of three gunmen killed by police on Friday after two sieges.
Tens of thousands of people have taken part in silent marches to remember the victims in Nice, Pau and Orleans.
President Francois Hollande has warned the danger is not over yet.
“We have to be vigilant. I also ask you to be united – it’s our best weapon,” said Mr Hollande in a televised address on Friday night.
The violence started on Wednesday when two brothers, Cherif and Said Kouachi, killed 12 people and injured 11 in an attack on the offices of satirical magazine Charlie Hebdo.
On Friday, the brothers were killed by police in Dammartin-en-Goele, 35km (22 miles) north of Paris, as they emerged from a besieged warehouse building firing at police.
One hostage had earlier been released and a second employee, who was hiding in the building’s cafeteria, was freed by police.
Local residents from Porte de Vincennes in Paris – where an armed man kept people hostage in a kosher grocery store – have given their reaction as the siege has ended
Police shortly afterwards launched an assault on a supermarket in eastern Paris where gunman Amedy Coulibaly had been holding several hostages.
Police killed Coulibaly and rescued 15 hostages. They found the bodies of four hostages who are believed to have been killed before the assault.
The four victims have been identified as Yoav Hattab, Philippe Braham, Yohan Cohen, and Francois-Michel Saada.
Police are searching for Hayat Boumeddiene, Coulibaly’s partner. She was said to be with Coulibaly when a policewoman was killed in Paris on Thursday, and is described as “armed and dangerous”.
(Source: BBC World)