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]

Separately, a building of the newspaper Hamburger Morgenpost, which like many other publications has reprinted Charlie Hebdo cartoons, was the target of an arson attack and two suspects were arrested, police said on Sunday.

Turkish and French sources said a woman hunted by French police as a suspect in the attacks had left France several days before the killings and is believed to be in Syria.

French police had launched in an intensive search for Hayat Boumeddiene, the 26-year-old partner of one of the attackers, describing her as "armed and dangerous".

But a source familiar with the situation said Boumeddiene left France last week and travelled to Syria via Turkey. A senior Turkish official corroborated that account, saying she passed through Istanbul on Jan. 2.