France's interior minister says "all measures" will be taken to prepare for what is expected to be a huge demonstration on January 11 to show unity against extremists.
Bernard Cazeneuve said on January 10 that the government was deploying hundreds of troops in addition to thousands of police and other security forces around Paris after three days of attacks by gunmen that has claimed 17 victims.
"I can already say that we have taken all necessary measures to guarantee the safety of the gathering so that those who want to go there could do that in complete safety," he said.
World leaders including Germany's Angela Merkel, Britain's David Cameron, and Ukrainian President Petro Poroshenko are among the many expected to join. Russian Foreign Minister Sergei Lavrov is also planning to attend.
Cazeneuve called for "extreme vigilance," saying that "given the context, we are exposed to risks."
He said some 700,000 people took part in marches across France on January 10 to remember the victims of this week's violence.
French PM: Intelligence Agency 'Failings'
The dramatic end to twin sieges on January 9 resulted on in the death of two brothers who had killed 12 people at the offices of the Charlie Hebdo satirical magazine on January 7.
French forces are hunting for the wife of Amedy Coulibaly, the gunman who also died on January 9 when security forces stormed a Jewish supermarket in eastern Paris where he had taken shoppers hostage.
Boumeddiene was said to be with Coulibaly when a policewoman was killed in Paris on January 8, and is described as "armed and dangerous."
Turkish intelligence sources were quoted as saying she entered Turkey on January 2 and may have crossed into Syria.
At a news conference, the brother of Ahmed Merabet, one of the police officers killed on January 7, said he was "Muslim and very proud of being a police officer and defending the values of the republic."
"He was killed by people who pretend to be Muslims. They are terrorists, that's it," he added.
In an address on January 9, Hollande called on the French people "to rise up this Sunday [January 11], together, to defend the values of democracy, freedom and pluralism to which we are attached."
But even as leaders urged the country to pull together, questions were also mounting over how the three men had slipped through the security net after it emerged that all three were known to the intelligence agencies.
French Prime Minister Manuel Valls acknowledged intelligence "failings" by security services that led to the deadly attack on Charlie Hebdo.
Valls said on BFMTV that the government had to analyze exactly what happened during the January 7 attack because "there was a failing, of course."
Several experts have said the attack might have been avoided if security officials had kept closer tabs on brothers Cherif and Said Kouachi, the prime suspects in the attack killed by security forces on January 9.
The French government knew the two had radical Islamist views and Said Kouachi was known to have spent time with the terrorist group Al-Qaeda in the Arabian Peninsula while in Yemen.
But some security experts say that with some 5,000 Islamists living in France it is impossible to keep track of all of them.
Police said Coulibaly was known to be an acquaintance of at least one of the Kouachi brothers.
Before he was shot dead by police, Coulibaly told the French station BFMTV by telephone that he had received instructions from the Islamic State group.
He said he wanted to defend Palestinians and target Jews.
BFMTV also spoke on the phone with Cherif Kouachi, who claimed to have been sent by Al-Qaeda in Yemen.
A senior Yemeni intelligence source as saying Said Kouachi, 34, had visited Yemen in 2011 and met the late Al-Qaeda preacher Anwar al-Awlaki during his stay.
Both Kouachis were on the United States' no-fly list of suspected terrorists.
Cherif Kouachi, 32, was convicted of terrorism charges in 2008 for his links to a network sending Islamic militants to fight against U.S. forces in Iraq.
Meanwhile, in an address to the nation, President Hollande called for "vigilance, unity, and mobilization."
He said: "We must demonstrate our determination to fight against everything that can divide us. And most importantly be implacable toward racism and anti-Semitism."
Muslim places of worship in several French towns have been targeted since the massacre at Charlie Hebdo.
The attacks, which have included shots being fired and blank grenades thrown, have not harmed anyone.
Valls has declared that France is at "war" with terrorism, but "not in a war against religion."
The Islamic State militant group has praised the Charlie Hebdo massacre, calling the gunmen "heroic jihadists."
With reporting by AFP and AP