French President Francois Hollande has described the tragedy as a terrorist attack.
A source close to the investigation said two men "armed with a Kalashnikov and a rocket-launcher" stormed the building in central Paris and "fire was exchanged with security forces." (Caught on Camera: the Gunmen Escaping After Charlie Hebdo Attack)
The source said gunmen had hijacked a car and knocked over a pedestrian as they sped away.
The satirical magazine 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. (Paris Attackers Shouted 'We Have Avenged the Prophet': Police)
Its offices were fire-bombed in November 2011 when it published a cartoon of Mohammed and under the title "Charia Hebdo".
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 controversial pictures of Prophet 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. (Don't Blame Muslims for Not Laughing at Our Cartoons, Editor Had Said)
French schools, consulates and cultural centres in 20 Muslim countries were briefly closed along with embassies for fear of retaliatory attacks.
Editor Stephane Charbonnier has received death threats and lives under police protection.