"I want to express my outrage at the despicable attack today against the French magazine Charlie Hebdo. It was a horrendous, unjustifiable and cold blooded crime. It was also a direct assault on a cornerstone of democracy, on the media and freedom of expression," Ban Ki-moon said.
"This is a moment for solidarity around the world. We must stand strong for freedom of expression and tolerance and stand against forces of division and hate," he added.
According to media reports, the attackers stated that they were linked to al-Qaeda.
Charlie Hebdo has previously been involved in a number of controversies involving radical Islamic fundamentalists. In particular, the magazine's former office was fire-bombed in 2011 after publishing controversial cartoons depicting the prophet Muhammad.