It was the first time Chirac has spoken publicly of nuclear action against foreign countries and he said France's doctrine of nuclear deterrence has now been extended to protect the country's strategic supplies, taken to mean oil.
Speaking during a visit to a French nuclear bas in Brittany, Chirac said: "Leaders of any state that uses terrorist means against us, as well as any that may be envisaging - in one way or another - using weapons of mass destruction, must understand that they would be exposing themselves to a firm and appropriate response on our behalf.
"That response could be conventional, it could also be of another nature," he said in a clear reference to nuclear weapons.
The president said he was extending the definition of "vital interests" protected by France's nuclear umbrella to include allies and "strategic supplies".
"Our world is marked by the emergence of affirmations of power that rely on the possession of nuclear, biological or chemical weapons"
The French press understood "strategic supplies" to include oil.
Le Monde newspaper said that was aimed at "probably also those countries from which France imports part of its energy needs".
"If, theoretically, such interests were threatened by regional powers - Iran, North Korea? - France would react," the paper said.
The French president, however, did not single out any country in his speech.
He did indicate, though, that the previous Cold War stance of threatening massive and widespread destruction against enemies had been changed to a doctrine permitting a graduated and limited nuclear response.
France has configured its nuclear arsenal to be able to respond "flexibly and reactively" to any threat, by reducing the number of nuclear heads on certain missiles on board its submarines, he said.
Chirac's comments have received
a mixed response at home
"Our world is marked by the emergence of affirmations of power that rely on the possession of nuclear, biological or chemical weapons," he said.
In an apparent reference to Iran, Chirac condemned "the temptation by certain countries to obtain nuclear capabilities in contravention of treaties".
Cold War echoes
There was mixed reaction to Chirac's statements.
In France the former prime minister Laurent Fabius, speaking on behalf of the Socialists, said there was nothing shocking about the position put forward.
But Helene Luc, a senator from the Communist Party and member of a defence committee, said: "This extension of the concept of nuclear dissuasion takes us back years to the Cold War and can only deepen tensions with countries that aspire to have such weapons."
The comments also provoked concerned reactions in Germany, from across the political spectrum and the press.
There was no official comment from Angela Merkel's coalition government but opposition MP Winfried Nachtwei said Chirac's comments were "totally adventurous" and "irresponsible".
Andreas Schockenhoff, the deputy president of Merkel's parliamentary party said in an interview on Friday with the regional daily Koelner Stadtanzeiger: "I fear that these comments will not help the international community achieve the highest level of solidarity."
"Chirac's threat is not only unwise, but also counterproductive"
The comments were also widely criticised in German newspapers.
Chirac's comment's are "clearly counterproductive," the economic daily Handelsblatt said.
The Westdeutsche Zeitung in Duesseldorf said: "Chirac's threat is not only unwise, but also counterproductive, because it leads to believe that diplomatic means are very limited in the face of nuclear ambitions."