The U.N. secretary-general is condemning the deadly attack on a French satirical newspaper as "a horrendous, unjustifiable and cold-blooded crime."

Ban Ki-moon spoke to the media hours after masked gunmen stormed the newspaper's Paris offices and killed 12 people, including the editor.

Ban called it "a very terrible terrorist attack" and expressed his outrage. He called it an "assault on a cornerstone of democracy."

He said: "This horrific attack was meant to divide. We must not fall into that trap. This is a moment of solidarity around the world."