France remains on the highest level of anti-terrorist alert on Monday and up to 5,000 special forces are patrolling outside Jewish schools, prime minister Manuel Valls told RMC Radio.
His comments come ahead of a crisis meeting of the French cabinet, chaired by French president Francois Hollande, to discuss security efforts after the government said the Paris attack suspects may have had accomplices.
The assault on the offices of satirical magazine Charlie Hebdo and separate attacks on police officers and a kosher supermarket killed 17 people.
The cabinet meeting also comes amid questions over how militants known to the authorities were able to launch the raids in Paris.
More than 1.5 million people marched in the French capital on Sunday in a show of unity.
The French government said the rally turnout was the highest on record. Across France, nearly four million people joined marches, according to an interior ministry estimate.
About 40 world leaders joined the start of the Paris march, linking arms in an act of solidarity.
They included British prime minister David Cameron, German chancellor Angela Merkel, Israeli prime minister Benjamin Netanyahu and Palestinian president Mahmoud Abbas.
Throughout the outpouring of fraternité the marchers remained good-natured.
Chants of “Char-lie. Char-lie” erupted, followed by ripples of applause. The same words were on every lips, on every placard: “Je suis Charlie. Nous sommes Charlie.”
Or, as paraphrased by Taoiseach Enda Kenny, who walked at the front of the march with President François Hollande and 50 other heads of state and government, “Nous sommes tous français aujourd’hui.”
Last Wednesday Chérif and Said Kouachi, sons of Algerian immigrants who claimed to represent al-Qaeda in the Arabian peninsula, massacred 12 people at the offices of the Charlie Hebdo satirical weekly.
The Kouachis’ accomplice, Ahmedi Coulibaly, the son of Malian immigrants and a follower of Islamic State, shot a policewoman dead on Thursday.
On Friday, the Kouachis and Coulibaly made their last stands, in an industrial zone north of Paris, and in a kosher supermarket where Coulibaly killed four Jewish hostages.
In all, the rampage claimed 17 French lives in three days. The marchers overcame fears of more attacks to join in the gathering. “Même pas peur - not even scared - appeared on many placards.
The march surpassed all expectations. According to the interior ministry, 3.7 million people marched in French cities, including more than 1.5 million in Paris.
Not even at the liberation of Paris from Nazi Germany had so many French people gone into the streets.
For a day, the French set their differences aside, finding unity in their attachment to the secular republic, and in their rejection of extremism.
The marchers vowed not to confuse extremism with Islam.
Additional reporting agencies