People light candles during a vigil, for the victims of a shooting by gunmen at the offices of weekly satirical magazine Charlie Hebdo in Paris, at the French consulate in Quebec City, January 7, 2015. [Photo/Agencies]

Some Parisians expressed fears about the effect of the attack on community relations in France, which has Europe's biggest Muslim population.

"This is bad for everyone - particularly for Muslims despite the fact that Islam is a fine religion. It risks making a bad situation worse," Cecile Electon, an arts worker who described herself as an atheist, told Reuters at a vigil on Paris's Place de la Republique attended by 35,000 people.

Charlie Hebdo (Charlie Weekly) is well known for courting controversy with satirical attacks on political and religious leaders of all faiths and has published numerous cartoons ridiculing the Prophet Mohammad. Jihadists online repeatedly warned that the magazine would pay for its ridicule.

The last tweet on its account mocked Abu Bakr al-Baghdadi, the leader of the militant Islamic State, which has taken control of large swathes of Iraq and Syria and called for "lone wolf" attacks on French soil.

There was no claim of responsibility. However, a witness quoted by 20 Minutes daily newspaper said one of the assailants cried out before getting into his car: "Tell the media that it is al Qaeda in Yemen!"

Supporters of Islamic State and other jihadist groups hailed the attack on Internet sites. Governments throughout Europe have expressed fear that fighters returning from Iraq or Syria could launch attacks in their home countries.

"Today the French Republic as a whole was the target," President Francois Hollande said in a prime-time evening television address. He declared a national day of mourning on Thursday.