Three heavily armed men have attacked a French satirical magazine based in Paris, killing at least 12 people, including four cartoonists and two policemen, officials have said.

The lawyer of the magazine confirmed that four cartoonists working with the publication, including the editor Stephane Charbonnier, known as 'Charb', were among the dead. Police said 11 people were wounded in the incident, adding that four were in a critical condition.

The cartoonists known as Cabu, Tignous and Wolinski were also killed in the attack, AFP news agency quoted a judicial source as saying.

Charlie Hebdo has drawn repeated threats for publishing caricatures of the Prophet Muhammad, among other controversial sketches.

French Interior Minister Bernard Cazeneuve said the assault was carried out by three attackers.

According to witnesses, one was a driver and the other two were attackers in terms of their role in the incident, police said.

In amateur camera footage shared on the internet, the attackers are heard shouting: "We have avenged the Prophet Mohammad."

The gunmen fled eastwards towards the suburbs, dumping their car in a residential area, police said. They then hijacked two other cars, wounded their drivers and ran over a pedestrian.

Al Jazeera's Jacky Rowland, reporting from Paris, said journalists and cartoonists reported several masked men dressed in black entering the building who then began to fire with automatic weapons.

"Some journalists took refuge on the roof," Rowland said.

"Charlie Hebdo has pushed boundaries in the past, and continues to challenge the idea of censorship."



President Francois Hollande, speaking outside the office of the magazine, described the attack as having been carried out by barbaric people.



"This is an attack on free speech." he told reporters. "No one can harm the spirit of this country which is this newspaper".

The magazine had tweeted a cartoon of Abu Bakr al-Baghdadi, the leader of the Islamic State in Iraq and the Levant (ISIL) group, minutes before the attack.Rowland said that a terrorism alert has been raised to its highest level in the wake of the attack.

France's Muslim leadership sharply condemned the shooting as a "barbaric" attack and an assault on press freedom and democracy.

"This extremely grave barbaric action is also an attack against democracy and the freedom of the press," the French Muslim Council (CFCM) said in a statement.

The body represents France's Muslim community, which is Europe's biggest and estimated to number between 3.5 million and five million people.

Hollande held a cabinet meeting at the Elysee Palace over the incident on Wednesday.

Huge crowds gathered in Paris and other major cities in France in a show of support for the staff of Charlie Hebdo.

Demonstrators in Paris were seen holding up banners in support of free speech, including one written, "Je suis Charlie (I am Charlie)", a slogan that has gone viral on social media.

French authorities said that school trips and all school outdoor activities have been cancelled until further notice while the gunmen are at large.

US President Barack Obama's spokesman said the US "condemns [the attack] in the strongest terms".

Josh Earnest said US officials have been in close contact to assist the French in the wake of the incident.

Earnest said the French have been "stalwart allies" in the US fight against the ISIL, adding: "We know they are not going to be cowed by this terrible act."

Various countries, including Russia, Qatar, Kuwait, Britain, Germany, Turkey, Saudi Arabia, Iran and Canada, have also condemned the attack.

In a 2012 interview, Charlie Hebdo editor Stephane Charbonnier told Al Jazeera why the magazine is a target.