After Charlie Hebdo Attack, Masked Gunmen Escape: 10 Facts

The national security alert system was set to "attack alert" following the killings in central Paris. (Track LIVE updates on Charlie Hebdo Attack)

French President Francois Hollande said "This is a terrorist attack, there is no doubt about it."

A source told news agency AFP that the gunmen had hijacked a car and knocked over a pedestrian while escaping.

The last tweet on Charlie Hebdo's account, posted minutes before the attack, mocked Abu Bakr al-Baghdadi, the leader of the Islamic State, which has taken control of large swathes of Iraq and Syria.

France is already on high alert after calls last year from Islamist militants to attack its citizens and interests in reprisal for French military strikes on Islamist strongholds in the Middle East and Africa.

Charlie Hebdo gained notoriety in February 2006 when it reprinted cartoons of the Prophet Mohammed that had originally appeared in Danish daily Jyllands-Posten, causing fury across the Muslim world.

Its offices were fire-bombed in November 2011 when it published a cartoon of Mohammed and under the title "Charia Hebdo". (Read More)

Despite being taken to court under anti-racism laws, the magazine continued to publish controversial cartoons of the Muslim prophet.

In September 2012 Charlie Hebdo published cartoons of a naked Mohammed as violent protests were taking place in several countries over a low-budget film, titled "Innocence of Muslims", which was made in the United States and insulted the prophet.

Editor Stephane Charbonnier, who had received death threats and was living under police protection, was among the 12 killed in the attack. The others killed have been identified as Jean Cabut, lead cartoonist at Charlie Hebdo, Bernard Velhac, cartoonist at Charlie Hebdo, Georges Wolinski, cartoonist at Charlie Hebdo and Bernard Maris, economist at Charlie Hebdo.