Washington (AFP) - US President Barack Obama condemned the "cowardly, evil" assault on a French satirical newspaper that left 12 dead Wednesday, pledging US assistance to Paris to bring the attackers to justice.
The US leader, speaking from the Oval Office, expressed solidarity with France and pledged that the attack on Charlie Hebdo would not squelch the right to free speech held dear by both nations.
"France is one of our oldest allies, our strongest allies," Obama said.
"For us to see the kind of cowardly, evil attacks that took place today, I think, reinforces once again why it's so important for us to stand in solidarity with them, just as they stand in solidarity with us."
"The fact that this was an attack on journalists, attack on our free press, also underscores the degree to which these terrorists fear freedom -- of speech and freedom of the press," he added.
"But the one thing that I'm very confident about is that the values that we share with the French people, a belief -- a universal belief in the freedom of expression -- is something that can't be silenced because of the senseless violence of the few."
Obama pledged to offer "every bit of assistance" possible to the French as the investigation of Wednesday's attack proceeds.
Gunmen shouting Islamist slogans stormed the offices of the Charlie Hebdo weekly in Paris, armed with an AK-47 assault rifle and a grenade launcher.
The weekly's editor Stephane Charbonnier and three renowned cartoonists were among those killed, officials said.
Charlie Hebdo had attracted controversy by publishing satirical cartoons of the Prophet Mohammed.
Secretary of State John Kerry -- a frequent visitor to Paris on his diplomatic travels -- said in French that he wanted to address the French people directly about the "murderous attack," saying: "All Americans stand by your side."
The "pen is an instrument of freedom, not fear," Kerry said.
"Free expression and a free press are core values... principles that can be attacked but never eradicated."
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Earlier, Obama had in a statement called the shooting "horrific" and praised France as a partner "in the fight against terrorists who threaten our shared security and the world."
Obama and Kerry met after the attack, the White House said, and FBI spokeswoman Minique Crump said that the agency had offered its expertise and was talking to its French counterparts.
"Currently we are conducting various database searches to provide our partners with any information available that may lead to the identification, apprehension, and ultimately prosecution of those responsible for this heinous crime," Crump said.
Obama's White House has not always been so supportive of Charlie Hebdo, however, and in September 2012 criticized its decision to go ahead and publish cartoons of the Prophet Mohammed.
"We don't question the right of something like this to be published. We just question the judgment behind the decision to publish it," then White House spokesman Jay Carney said.
Carney was speaking at a time of heightened tension when US embassies in the Muslim world had come under attack by locals angered by the portrayal of their religion in Western media.
Still, on Wednesday, US officials were unanimous in their condemnation of the attack and in their solidarity with France.
The US embassy in Paris symbolically changed its Twitter profile picture to a newly popular slogan inspired by the attack: "Je suis Charlie" (I am Charlie).
Kerry also vowed that "the murderers dare proclaim Charlie Hebdo is dead, but make no mistake -- they are wrong."
"Today, tomorrow, in Paris, in France, the freedom of expression that this magazine... represented is not able to be killed by this kind of act of terror."
In New York, Mayor Bill de Blasio asked for a moment of silence for the victims.