French Foreign Minister Bernard Kouchner gave the warning on Sunday, a sign of a toughening stance by his country in the West's efforts to rein in Iran's nuclear program. Tehran denies any intention to build a bomb.
"We do not take these threats seriously," Ahmadinejad said, according to Iran's state news agency IRNA. "Media speculations are different from real words and we do not take these remarks seriously."
IRNA on Monday criticized Kouchner in an editorial, saying France was taking an "even more inflammatory and more illogical" tone than the United States, which has pushed for tougher action on Iran.
Kouchner said that if "such a bomb is made ... we must prepare ourselves for the worst," specifying that could mean a war. He said European leaders were considering their own economic sanctions against the Islamic country.
The U.N. has imposed limited sanctions on Iran for its refusal to halt uranium enrichment. The U.S. and its allies accuse Tehran of seeking to develop nuclear weapons, but Iran insists its program aims only to generate electricity.