NATO Secretary General Jens Stoltenberg on Wednesday strongly condemned the deadly terrorist attack on a magazine office in Paris.

"This was a barbaric act and an outrageous attack on press freedom. My thoughts are with the victims and their families," Stoltenberg said in a statement.

Noting the NATO stands in full solidarity with France, he said all NATO Allies stand together in the fight against terrorism.

"Terrorism in all its forms and manifestations can never be tolerated or justified," he said.

Three masked and heavily armed men stormed the offices of the satirical weekly Charlie Hebdo, earlier in the day, killing at least 12 people, including two policemen.