France has vowed to intensify its ongoing airstrikes against Islamic State (Isis) in Syria and Iraq after a series of terror attacks rocked its capital Paris. French Prime Minister Manuel Valls has declared "we are at war", after 129 people were killed by suspected Isis terrorists.

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In the wake of the stepped up anti-terror measures in France, authorities have promised to "destroy" IS targets, who masterminded the terror attack on French soil -- the worst assault since World War II.

Valls told TF1 television: "We are at war, and because we are at war we are taking exceptional measures. We will win this war." He insisted that French forces would not only wipe Islamist targets in France, but also in the Middle East. He repeated the comments on social media as well.

Valls was echoing the comments earlier made by President Francois Hollande, who said that Isis were "a terrorist army... a jihadist army, against France, against the values that we defend everywhere in the world, against what we are: A free country that means something to the whole planet".

France is part of the US-led coalition forces, who are pounding Isis interests in conflict zones. They have been targeting Isis camps and the Islamist group claimed that the latest terror attacks were in response to the airstrikes.

The extremist group said: "The stench of death will not leave their noses as long as they remain at the forefront of the Crusaders' campaign, dare to curse our prophet, boast of a war on Islam in France, and strike Muslims in the lands of the caliphate with warplanes."