Gunmen have attacked the Paris office of French satirical magazine Charlie Hebdo, killing 12 people and injuring seven in an apparent Islamist attack.
At least two masked attackers opened fire with assault rifles in the office and exchanged shots with police in the street outside before escaping by car.
The gunmen shouted "we have avenged the Prophet Muhammad", witnesses say.
President Francois Hollande said there was no doubt it had been a terrorist attack "of exceptional barbarity".
A major police operation is under way in the Paris area to catch the killers.
French President Francois Hollande: "This is an act of exceptional barbarism"
The satirical weekly has courted controversy in the past with its irreverent take on news and current affairs. It was fire-bombed in November 2011 a day after it carried a caricature of the Prophet Muhammad.
The latest tweet on Charlie Hebdo's account was a cartoon of the Islamic State militant group leader, Abu Bakr al-Baghdadi.
A witness filmed the scene as the sound of gunshots were heard
People had been "murdered in a cowardly manner", President Hollande told reporters at the scene. "We are threatened because we are a country of liberty," he added, appealing for national unity.
UK Prime Minister David Cameron said in a tweet: "The murders in Paris are sickening. We stand with the French people in the fight against terror and defending the freedom of the press."