TEN journalists and two police officers were shot dead today by masked gunmen in an attack on French satirical newspaper Charlie Hebdo.

The dead included editor Stephane Charbonnier and several leading cartoonists.

Video footage showed the attackers shouting “Allahu akbar (God is great)” as they stormed the paper’s Paris headquarters with assault rifles.

The attack follows threats from the Islamic State (Isis) terrorist movement to launch attacks on France and it came minutes after the paper tweeted a cartoon of Isis chief Abu Bakr al-Baghdadi.

Police union SBP said the men escaped in two vehicles.

France raised its security alert to the highest level possible and the government ordered reinforced security at places of worship, shops, bus, train and metro stations and other media outlets.

Reporters Without Borders’s Christophe DeLoire said the gunmen went to the second floor and fired indiscriminately at working journalists.

“This is the darkest day in the history of the French press,” he said.

French journalists’ union SNJ said there were “no words strong enough to express the sadness and anger of the profession today.

“It is freedom of expression that is being murdered.”

The union pointed out that the number of journalists killed for doing their jobs has risen dramatically over the past year.

Britain’s National Union of Journalists general secretary Michelle Stanistreet said: “Supporters of civil liberties must stand together with governments to condemn this act and defend the right of all journalists to do their job without fear of threats, intimidation and murder.”

French Communist Party leader Pierre Laurent said he was “stupefied” by the carnage and expressed the party’s solidarity with the newspaper’s staff and the relatives of the victims.

“Nothing can justify this murderous madness,” he said.

Charlie Hebdo had been targeted before for publishing caricatures of the Muslim prophet Mohammed, which are considered offensive by many of the religion’s adherents.

But the savagery of yesterday’s attack will raise fears that young people who have travelled from Europe to join Isis’s war against the Iraqi and Syrian governments — waged in the latter country with the connivance of Western countries hostile to Bashar al-Assad’s regime — are returning trained and prepared to launch terrorist assaults at home.