French authorities have deployed 500 extra troops around Paris after three days of terror in the 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 January 9 after two sieges.
More than 210,000 people have taken part in silent marches across France to remember the victims.
After a security cabinet meeting on January 10, Bernard Cazeneuve said France would remain on its highest state of alert “for the next few weeks”.
He promised tight security for a massive unity march in Paris on January 11.
Those set to attend Sunday’s unity rally include UK PM David Cameron, German Chancellor Angela Merkel, Turkish PM Ahmet Davutoglu, Spanish PM Mariano Rajoy and Russian Foreign Minister Sergei Lavrov.
“Sunday, the French people will cry out their love of liberty,” said PM Manuel Valls.
France would be “firm and relentless in the face of the enemies of liberty”, he added, urging all people to “assume their responsibilities”.
Silent marches have held in cities including Paris, Orleans, Nice, Pau, Toulouse and Nantes to remember the victims of this week’s violence.
Some protesters held banners that read “I am against racism”, “unite”, or “I am Charlie”, in reference to Charlie Hebo, the satirical magazine whose offices were attacked on January 7.
The family of Ahmed Merabet, one of the police officers killed during the Charlie Hebdo attack, gave an emotional news conference on January 10.
Ahmed Merabet was “Muslim, and very proud of being a police officer and defending the values of the Republic”, his brother Malek Merabet said.
He added that the family was “devastated by this act of barbarity, and shared the pain of the families of all the victims”.
“I want to say to all the racist, Islamophobic, anti-Semitic people, that one must not amalgamate extremists and Muslims,” Ahmed Merabet’s brother added.
The family said they were “proud” of the gatherings that had taken place to commemorate the victims, saying they proved that France could be united.
The violence began when two brothers, Cherif and Said Kouachi, killed 12 people and injured 11 in an attack on the offices of Charlie Hebdo magazine on January 7.
On Janaury 9, Cherif and Said Kouachi were killed by police in Dammartin-en-Goele, 22 miles north of Paris, as they emerged from a besieged warehouse building firing their automatic weapons.
One hostage had earlier been released and a second employee, who was hiding in the building’s cafeteria, was freed by police.
Police shortly afterwards launched an assault on a supermarket in eastern Paris where gunman Amedy Coulibaly had been holding several hostages.
Police killed Amedy 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. Their names were released by the Representative Council of French Jewish Institutions.
Police are searching for Hayat Boumeddiene, Amedy Coulibaly’s girlfriend. She was said to be with Amedy Coulibaly when a policewoman was killed in Paris on Thursday, and is described as “armed and dangerous”.
Security officials have said they were aware of Amedy Coulibaly and the Kouachi brothers. Said Kouachi was known to have travelled to Yemen in 2011.
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