"It's hard to imagine what that could do to the region."
For his part, Kouchner called for "precise sanctions" against Iran and acknowledged that France and Russia had differences on the issue.
"The countries that feel threatened ... should prepare for defence, and even counterattack"
Adolfo Talpalar, Stockholm, Sweden
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"The worst thing to happen would be a war, and in order to avoid it, we need to continue talks, and be firm enough regarding sanctions," he said.
"We have to work on precise sanctions that would demonstrate the world community's serious approach to this problem."
Kouchner is on his first trip to Moscow as foreign minister.
His warning over the weekend that the world must be prepared for the possibility of war if Iran obtains atomic weapons, provoked strong reactions.
In an interview with a French newspaper, Kouchner sought, however, to play down his remarks, saying they were meant as a "message of peace".
He told Le Monde: "I do not want it to be said that I am a warmonger!"
During Tuesday's meeting with Kouchner, Lavrov also criticised the idea of unilateral sanctions against Tehran by the EU or the US.
|Russia is helping to build Iranian nuclear|
facilities in Bushehr in the south [EPA]
"If we agreed to work collectively and that is represented in collective decisions made by the UN Security Council, then what purpose would unilateral sanctions have?"
Lavrov and Kouchner met in advance of a UN Security Council meeting on Friday that could impose new sanctions against the Islamic republic for its controversial uranium-enrichment activity.
Pressure on Iran has escalated in the run-up to the meeting, though the country's president says he is unconcerned by Kouchner's remarks.
"We do not take these declarations seriously," Mahmoud Ahmadinejad said on Tuesday. "Comments to the media are different from the real positions."
Tehran denies US accusations it is seeking an atomic weapon, saying its nuclear programme is aimed at generating electricity.
Iran has yet to comply with repeated UN demands that it suspend uranium enrichment and other sensitive work that could potentially be used in producing weapons.
Russia, which is building Iran's first nuclear reactor in the southern Iranian city of Bushehr, has consistently warned against attacking Iran.