Speaking a day after the biggest French public demonstration ever recorded, in honour of the victims, Defence Minister Jean-Yves Le Drian said the country remained at risk of further attacks. Soldiers would guard transport hubs, tourism sites and key buildings and mount general street patrols.
"The threats remain and we have to protect ourselves from them. It is an internal operation that will mobilise almost as many men as we have in our overseas operations," Le Drian told reporters after a cabinet meeting.
The victims, including journalists and police, died in three days of violence that began on Wednesday (local time) with a shooting attack on the political weekly Charlie Hebdo, known for its satirical attacks on Islam and other religions. Many at Sunday's march wore badges and carried placards declaring "I Am Charlie".
The Charlie Hebdo attackers, two French-born brothers of Algerian origin, singled out the weekly for its publication of cartoons depicting and ridiculing the Prophet Mohammad.
Charlie Hebdo's remaining members are working on an eight page issue due to come out on Wednesday with a one-million copy print run. Its lawyer, Richard Malka, told France Info radio there would be caricatures of the Prophet Mohammad.
"We will not give in. The spirit of 'I am Charlie' means the right to blaspheme ," he said, adding that the front page would be released on Monday evening.
The three days of bloodshed ended on Friday with a hostage-taking at a Jewish deli in Paris where four hostages and another gunman were killed. That gunman declared allegiance to Islamic State insurgents and said he was acting in response to French military deployments against militant Islamist groups overseas.
Interior Minister Bernard Cazeneuve said 4700 police officers would be placed at all 717 Jewish schools across the country in addition to some 4100 gendarmes already deployed.
"Synagogues, Jewish schools, but also mosques will be protected because in the past few days there have been a number of attacks against mosques," Prime Minister Manuel Valls told BFM TV.
France has Europe's largest Muslim and Jewish communities.
The first two attackers, who had travelled to Yemen in 2011 for training, were killed on Friday after a siege north of the capital. Police said all three men were part of the same Paris-based militant Islamist cell.
About 1.5 million people marched in Paris on Sunday and 2.5 million more in the provinces. The Paris march was led by dozens of foreign leaders. Some commentators said the last time crowds of this size were seen in the capital was at the Liberation of Paris from Nazi Germany in 1944.
SEARCH FOR ACCOMPLICES
The co-ordinated assaults amounted to the deadliest attack by militant Islamists on a European city since four suicide bombers killed 52 in attacks on London's transport system in 2005.
Valls said police were searching for likely accomplices of the French cell. The Turkish government confirmed that the female companion of the supermarket attacker had entered Syria on Jan. 8 from Turkey, having arrived in Istanbul several days before the killings.
After an emergency cabinet meeting on Monday to outline Britain's response to the attacks, British Prime Minister David Cameron pledged to give security and intelligence services new powers to monitor Internet communications.
German Chancellor Angela Merkel, Italian Prime Minister Matteo Renzi and Cameron were among 44 foreign leaders marching with French President Francois Hollande on Sunday.
Israel's Benjamin Netanyahu and Palestinian President Mahmoud Abbas were also present and walked just a few steps from one another.
Netanyahu visited the Jewish supermarket, scene of the hostage taking, on Monday with about 300 people shouting "BB" and singing the French and Israeli national anthems.
His invitation to French Jews to migrate to Israel if they wanted irritated some. Valls scrambled to reassure the community it was safe and an integral part of France.
"It was essential he came to show that he was with us French, Jews of France," said Mauricette Abouchaya. "(But) we're in France, we want to stay in France. It is our country."
With growing calls for a comprehensive investigation into whether there had been security failings given that the three gunmen were known to intelligence services, Valls and main opposition leader Nicolas Sarkozy agreed on a bi-partisan parliamentary commission into the attacks.
Valls also said the government had begun studying ways to strengthen the fight against "homegrown terrorism". France strenghtened anti-terrorism legislation last year to prevent its nationals travelling to Syria and Iraq.
The prime minister said one proposal being studied was to isolate radical Islamist inmates from others in the nation's prisons, as repeated cases showed individuals were susceptible to radicalisation in jail.
"There is a lot of work to be done in the prisons. It's a priority," Valls said.
