Sarkozy was speaking at a G20 summit of world leaders days before the scheduled release of a United Nations report expected to offer intelligence pointing to possible military dimensions of Iran's nuclear program.
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The report, however, is expected to stop short of declaring that Iran is attempting to develop nuclear weapons.
"Iran's behavior and this obssessional desire to acquire nuclear military (capability) is in violation of all international rules, and France condemns firmly the lack of respect for these rules," he said in the French Riviera resort of Cannes.
"If Israel's existence were threatened, France would not stand idly by."
- Western powers, including Israel, suspect Tehran of developing nuclear weapons - something Iran denies - and have imposed sanctions in an attempt to curb its program.
The United States and Israel have repeatedly hinted at possible use of force against Iranian nuclear sites, drawing threats of fierce retaliation from the Islamic Republic.
"The State of Israel cannot be destroyed," he told Ynet. "An attack on Iran could affect not only Israel, but the entire region for 100 years."
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