French President Francois Hollande said on Saturday the attacks in Paris that killed 127 people were "an act of war" organised from abroad by Islamic State with internal help.
"Faced with war, the country must take appropriate action," he said, without saying what that meant.
Hollande said he would address parliament on Monday in an extraordinary meeting and the country would observe three days of official mourning for the victims of Friday's attacks.
The attacks at a stadium, concert hall and cafes and restaurants in northern and eastern Paris were "an act of war committed by Daesh that was prepared, organised and planned from outside (of France)" with help from inside France, Hollande said, using the Arabic acronym for Islamic State.
"All measures to protect our compatriots and our territory are being taken within the framework of the state of emergency," he said.
Islamic State released an undated video on Saturday urging Muslims to attack France.
The coordinated assault on Friday evening came as France, a founder member of the U.S.-led coalition waging air strikes against Islamic State fighters in Syria and Iraq, was on high alert for terrorist attacks ahead of a global climate conference due to open later this month.
The deadliest attack was on the Bataclan, a popular concert venue where the Californian rock group Eagles of Death Metal was performing. The concert hall is just a few hundred metres from the former offices of the satirical weekly Charlie Hebdo, target of a deadly attack by Islamist gunmen in January.
Some witnesses in the hall said they heard the gunmen shout Islamic chants and slogans condemning France's role in Syria.