Several thousand people walk behind a banner as they march to pay tribute to the victims following a shooting Wednesday by gunmen at the office of the offices of the satirical weekly newspaper Charlie Hebdo during a demonstration in Nantes January 10, 2015. [Photo/Agencies]

Meanwhile, Turkish and French sources said that 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 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.

A senior Turkish security official said Paris and Ankara were now cooperating in trying to trace her but that she had arrived in Istanbul without any warning from France.

"We think she is in Syria at the moment but we do not have any evidence about that. She is most probably not in Turkey," the Turkish source said.