"We have to prepare for the worst, and the worst, sir, is war," Kouchner said in an interview on LCI television and RTL radio.
Kouchner's comments follow a similarly hawkish statement by French President Nicolas Sarkozy, who said last month in his first major foreign policy speech since taking office that a diplomatic push by the world's powers was the only alternative to "an Iranian bomb or the bombing of Iran."
France has said repeatedly it wants the United Nations Security Council to pass tougher sanctions against Iran over its failure to dispel fears that it is secretly pursuing nuclear weapons.
"We do not want to signal anything other than 'peace is in your interest, and in ours too,'" Kouchner said.
Asked whether he believed U.S. President George W. Bush would launch air strikes against Iran before the end of his term of office, he said: "Honestly, I don't think we've reached that stage, not at all. At least I hope so."
Kouchner also said Sunday that France had advised its large companies not to respond to tenders in Iran and repeated a call for greater pressure on Tehran over its nuclear program.
The French foreign minister said the companies that had been contacted were free to decide what to do.
"We have already asked a certain number of our large companies to not respond to tenders, and it is a way of signalling that we are serious," Kouchner said.
"We are not banning French companies from submitting. We have advised them not to. These are private companies. But I think that it has been heard and we are not the only ones to have done this."
Iranian minister: Russian nuclear fuel ready to ship to Iran
Enriched uranium fuel is ready to be shipped from Russia to Iran's first nuclear power plant, state television on Sunday quoted Iran's foreign minister as saying.
The announcement comes after talks in Moscow between minister Manouchehr Mottaki and Russian nuclear chief Sergei Kiriyenko to address delays in completing the US$1 billion (720 million) joint Iranian-Russian Bushehr power plant.
Nuclear fuel for this power plant, inspected and sealed by the International Atomic Energy Agency, is ready, the broadcast quoted Mottaki as saying late on Saturday. We do see the trend of cooperation between Iran and Russia moving ahead for the Bushehr power plant.
The project, Iran's first nuclear power plant, has been beset by repeated delays due to payment problems on the Iranian side, according to the Russians. Tehran, however, maintains it is because Moscow has been caving into Western pressure to halt the project.
The United States maintains that Iran's nuclear power program is a cover for developing weapons and has called for further sanctions, while Tehran denies the charges and insists it just wants to master the technology to meet future power needs under the provisions of the Nuclear Nonproliferation Treaty.
While Russia has continued to oppose a U.S. push for tougher sanctions against Tehran, Russian officials have shown growing irritation with Iran's refusal to freeze its own uranium enrichment effort. Moscow appears to be using its control over the Bushehr project to press Iran for concessions on its nuclear program.
A European diplomat last month said that Moscow had warned Tehran it would not deliver fuel to the plant unless Tehran lifts the veil of secrecy on suspicious past atomic activities. The IAEA has since reported increased cooperation from the Iranians over its program.
Russian officials say the plant cannot open until six months after fuel is delivered.
Enriched to a low degree, uranium is used as a reactor fuel; higher enrichment creates material for a nuclear warhead.
In a separate report, state television said that Iranian President Mahmoud Ahmadinejad had offered his country's nuclear experience to Saudi Arabia.