French President Francois Hollande is due to chair a crisis meeting with cabinet ministers on national security after last week's deadly attacks.
The meeting comes amid questions over how militants known to the authorities were able to launch the raids in Paris.
The assault on the offices of satirical magazine Charlie Hebdo and separate attacks on police officers and a kosher supermarket killed 17 people.
More than 1.5m people marched in the capital on Sunday in a show of unity.
The French government said the rally turnout was the highest on record.
About 40 world leaders joined the start of the Paris march, linking arms in an act of solidarity.
They included UK Prime Minister David Cameron, German Chancellor Angela Merkel, Israeli Prime Minister Benjamin Netanyahu and Palestinian President Mahmoud Abbas.
President Hollande will meet his cabinet, including Prime Minister Manuel Valls and Interior Minister Bernard Cazeneuve, as well as the heads of police and security services at 08:30 local time (07:30 GMT) on Monday.
In London, Prime Minister Cameron is also consulting senior intelligence and security officials over Britain's response to the attacks in France.
Last week, Valls admitted there had been "clear failings" after it emerged that the three gunman involved in the attacks - Said and Cherif Kouachi and Amedy Coulibaly - had a history of extremism.
The Kouachi brothers were on UK and US terror watch lists and Coulibaly had previously been convicted for plotting to free a known militant from prison. Coulibaly met Cherif Kouachi while in jail.
Coulibaly and the two brothers were shot dead on Friday after police ended two separate sieges.
Ahead of Sunday's rally in Paris, a video emerged appearing to show Coulibaly pledging allegiance to the Islamic State militant group.
In the video, he said he was working with the Kouachi brothers: "We have split our team into two... to increase the impact of our actions."
Coulibaly killed four people at a kosher supermarket in eastern Paris on Friday before police stormed the building.
He is also believed to have shot dead a policewoman the day before.
The attacks in Paris started last Wednesday, when the Kouachi brothers raided the offices of the satirical magazine Charlie Hebdo, killing 12 people - including eight journalists and two police officers.
President Hollande warned France to remain vigilant on Friday, saying the country faced further threats.
French police are still hunting for accomplices of the three gunmen, including Hayat Boumeddiene, Coulibaly's partner.
However, officials in Turkey believe she may have travelled through the country en route to Syria before the attacks in Paris unfolded.
Interior Minister Cazeneuve said France would remain on high alert in the coming weeks.
He hosted a meeting on Sunday morning of fellow interior ministers from across Europe, including the UK's Theresa May, to discuss the threat posed by militants.
Following the meeting, the ministers issued a statement saying that greater internet and borders surveillance was needed to combat terrorist attacks.
