French President Jacques Chirac has said France would be ready to use nuclear weapons against any state which launched a terrorist attack against it.
Chirac warned of new threats in a post-Cold War world
Speaking at a nuclear submarine base in north-western France, Mr Chirac said a French response "could be conventional. It could also be of another nature."
He said France's nuclear forces had been configured for such an event.
France has had an independent nuclear deterrent since 1960, after an arms programme ordered by Charles de Gaulle.
The BBC's Alistair Sandford in Paris says this is the first time that Mr Chirac has so clearly linked the threat of a nuclear response to a terrorist attack.
On a visit to L'Ile-Longue base in Brittany, Mr Chirac said leaders of states who would "use terrorist means against us, just like anyone who would envisage using, in one way or another, arms of mass destruction, must understand that they would expose themselves to a firm and adapted response from us".
The president spoke of new threats in a post-Cold War world, without mentioning any specific threat against France.
"In numerous countries, radical ideas are spreading, advocating a confrontation of civilisations," he said, adding that "odious attacks" could escalate to "other yet more serious forms involving states".
Following the end of the Cold War, France scaled down its nuclear deterrent, scrapping a number of missile systems.
It is believed to have a current arsenal of around 350 nuclear weapons.