Paris was in lockdown last night as the hunt for the gunmen behind France's worst terrorist attack continued.
welve people were killed when gunmen stormed the offices of Charlie Hebdo, a satirical magazine that has a reputation for poking fun at the powerful and pompous.
In recent years the magazine has published cartoons depicting the Prophet Mohammed, which has outraged Islamists who have threatened reprisals.
The three gunmen were still on the run last night as the authorities raised the threat level to its highest point.
The suspected gunmen were reported to be French-Algerian brothers Cherif and Said Kouachi, aged 32 and 34. They are from Paris and have links to extremists in Iraq and Syria.
The youngest suspect is Hamid Mourad, a homeless 18-year-old of unknown nationality.
France has been chilled by the savagery - and apparent professionalism - of the assault on the magazine's office in the heart of Paris yesterday morning, which left four of the country's best-known cartoonists dead.
Two policemen were also killed - one of them murdered as he lay on the ground. The hooded gunmen said that they were taking revenge for the magazine's record of lampooning the Prophet Mohammed and extremist Islamism.
Twenty other people were seriously injured.
With the gunmen still on the loose there are fears of further attacks in the coming days. More than 3,000 policeman and soldiers were hunting for the killers and protecting potential targets in the Paris area last night.
The attack on Charlie Hebdo had been well-planned. The gunmen, wearing black military fatigues, burst into the magazine's offices in the 11th arrondissement near Bastille at 11.30am during the weekly editorial meeting.
They had chosen the only time in the week when there are more than two or three people present. They opened fire with Kalashnikov-type automatic weapons.
Outside, a police security guard was shot dead and another policeman was initially wounded in a shootout with the gunmen in a nearby street as they escaped. A chilling video posted on the internet showed one of the attackers calmly strolling over to the policeman to shoot him in the head as he lay on the ground.
Another Charlie Hebdo cartoonist, Coco, who escaped unharmed, said that the killers spoke perfect French and claimed to have been "sent by al-Qaida".
In an amateur video clip, the gunmen are heard shouting: "We have killed Charlie Hebdo. We have avenged the Prophet Mohammed." Other witnesses said they also shouted "Allahu Akbar" (God is great).
The gunmen escaped in a black Citroen, which was abandoned a mile away, and are believed to have hijacked another car.
Ten people were killed in Charlie Hebdo including the magazine's editor and chief cartoonist Stéphane Charbonnier (47), known as 'Charb'. Other victims included magazine founder Jean Cabut (76), one of France's most beloved cartoonists. Veteran cartoonist Georges Wolinski (83) was among the dead, as well as economist and television personality Bernard Maris (68).