Hundreds of thousands of people gather on the Place de la Republique to attend the solidarity march (Rassemblement Republicain) in the streets of Paris January 11, 2015.[Photo/Agencies]

"I am here to show the terrorists they have not won - on the contrary, it is bringing people together of all religions," said Zakaria Moumni, a 34-year-old Franco-Moroccan draped in the French flag.

Loris Peres, 12, there with his mother and brother, said: "For me this is like paying respect to your loved ones, as if it were family ... We did a lesson about this at school."

German Chancellor Angela Merkel, British Prime Minister David Cameron and Italy Prime Minister Matteo Renzi will be among 44 foreign leaders due to march with President Francois Hollande. U.N. Secretary-General Ban Ki-moon, Turkish premier Ahmet Davutoglu and Israel's Benjamin Netanyahu - who earlier encouraged French Jews to emigrate to Israel - are expected.

"(The march) will be an unprecedented demonstration that will be go down in the history books," Prime Minister Manuel Valls said.

Twelve people were killed in Wednesday's initial attack on Charlie Hebdo, a journal know for satirising religions and politicians. The attackers, two French-born brothers of Algerian origin, singled out the weekly for its publication of cartoons depicting and ridiculing the Prophet Mohammad.

All three gunmen were killed in what local commentators have called "France's 9/11", a reference to the September 2001 attacks on U.S. targets by al Qaeda.

Across France on Saturday, hundreds of thousands of people took part in rallies. Many carried signs saying "Je suis Charlie" (I am Charlie).

The head of France's 550,000-strong Jewish community, Roger Cukierman, the largest in Europe, said Hollande had promised that Jewish schools and synagogues would have extra protection, by the army if necessary, after the killings.