Francois Hollande says it is an act of war.
Via NY Times:
The Islamic State claimed responsibility on Saturday for the catastrophic attacks in the French capital, calling them “the first of the storm” and mocking France as a “capital of prostitution and obscenity,” according to statements released in multiple languages on one of the terror group’s encrypted messaging accounts.
The remarks came in a communiqué published in Arabic, English and French on the Islamic State’s Telegram account and then distributed via their supporters on Twitter, according to a transcript provided by the SITE Intelligence Group, which tracks jihadist propaganda.