Russia is unlikely to support new U.N. sanctions against Iran over its nuclear program until after the U.N. atomic watchdog's latest study of Iran's activities, which may not be completed until December, the French foreign minister said on Thursday.

"I think it would very difficult to convince the Russians and the Chinese before (then)," French Foreign Minister Bernard Kouchner said at a breakfast with reporters.

"For the time being it is difficult to foresee," said Kouchner, who said he had spent hours trying in vain to persuade Russian Foreign Minister Sergei Lavrov to join western states in a new round of tighter sanctions against Iran.

Iran last month agreed to explain the scope of its nuclear program to the International Atomic Energy Agency, but critics say the deal allows Tehran to address issues one by one in a long-drawn-out process which could last until December.

The United States, France and other allies want the U.N. Security Council to agree tougher sanctions against Tehran over its refusal to suspend uranium enrichment, which the West suspects is cover for bomb making. Iran says its program is for generating nuclear power.

Russia and China previously voted for two sets of punitive measures, but Lavrov told two reporters earlier in the week that "the third track" of fresh sanctions was an invention "by the Americans and the French, not us."

Russia, backed by China, has not flatly refused to allow the issue to return to the Security Council but diplomats said Lavrov has not engaged in any of the discussions this week on what a new set of sanctions would entail. Both Russia and China have veto power in the Security Council.

British Foreign Minister David Miliband, in briefing reporters, stressed the importance of unity among the major powers, the United States, Russia, China, France, Britain and Germany, which would negotiate a resolution.

"The most important thing is that the unanimity of the international community is valued by all six (powers) and sends a very clear signal to Iran and we need to keep that going."

Asked about U.S. and French calls for sanctions outside the Security Council, Miliband said: "It's already the case that European Union countries have taken greater action than was required by the Security Council. That is healthy and good."

He said companies and banks were making their own decisions about investment based on the political risk.

"The figures on the fall in European investment in Iran in the first 6 months of this year are spectacular," he said, citing a 40 percent decrease. "There is evidence of sanctions having an effect."

But Lavrov, speaking at a meeting of major powers alongside the General Assembly, on Wednesday condemned Western moves to take unilateral sanctions outside the U.N. framework if the Security Council was deadlocked, meeting participants said.

Iranian President Mahmoud Ahmadinejad told the Assembly on Tuesday that the issue of his country's nuclear ambitions was "closed" and was now to be handled by the IAEA.