MOSCOW (Combined Sources)-Russian Foreign Minister Sergei Lavrov voiced doubt on Thursday about whether Tehran would fulfill the terms of a deal brokered by Brazil and Turkey aimed at resolving the Iranian nuclear crisis.

"There are no 100 percent guarantees. Very much will depend on how Iran will approach its commitments. If it strictly abides by them, Russia will actively support the scheme proposed by Brazil and Turkey," Lavrov said.

"Despite Russia's years of efforts to resolve the nuclear dispute, the response from the Iranian side has been unsatisfactory," he added in comments that indicated growing dismay with Iran in Russia.

After years of resistance, Russia is now supporting possible new sanctions against Iran over concern that it is developing nuclear weapons. Iranian President Mahmoud Ahmadinejad took Russia to task for this on Wednesday, saying it was difficult to gauge whether the Kremlin was a friend or an enemy. "This statement is being interpreted as emotional," Lavrov said at a news conference in Moscow.

Moscow, like Washington, has reacted coolly to the nuclear fuel deal aimed at defusing the standoff that was brokered by Brazil and Turkey earlier this month, a stance that has clearly disappointed Tehran.

Russian President Dmitry Medvedev cautiously welcomed the deal but also expressed concern that it might fail to allay the main fear of the international community about Tehran's uranium enrichment operations.

Delivering an extraordinary broadside against a country that has traditionally been seen as enjoying the closest political ties to Tehran of any major world power, Iranian President Mahmoud Ahmadinejad launched a stinging attack against Russia on Wednesday, accusing it of "siding with those who have been our enemy for 30 years."

"The Tehran declaration (on a fuel swap) is the best opportunity. We took an important step and said something very important. There are no excuses left," Ahmadinejad said in the speech addressed to U.S. and Russian leaders.

"Today it has become very difficult to explain Mr. Medvedev's behavior to our people. Iranians do not understand whether they are our neighbor and friend standing by our side or are after other things," he said in the speech delivered in the southeastern city of Kerman.

"We hope Russian officials will pay attention, make amends and not let Iranians put them in line with their historic enemies. If I were in the Russian president's shoes I would be more cautious in commenting and decision making about issues pertaining to the great and strong nation of Iran."

Signed last week, the Brazil-Turkey-brokered nuclear swap deal calls for Iran to deposit a large part of its uranium stockpile in Turkey in exchange for better-enriched nuclear fuel destined for a research reactor in Tehran.

Expressing frustration with Iran in the standoff over its nuclear program, Lavrov gave no indication of how the deal might affect Russia's stance on a U.S.-drafted resolution in the U.N. Security Council calling for Iran to be punished with a new round of sanctions. "There are no 100 percent guarantees. Very much will depend on how Iran will approach its commitments. If it strictly abides by them, Russia will actively support the scheme proposed by Brazil and Turkey," Lavrov said.

"We welcome this deal. If fully implemented, it will create very important preconditions not just for the solution of the concrete problem - supplies of fuel for this reactor - but for improving the atmosphere for the renewal of negotiations," Lavrov added in televised remarks.

On Monday, Iran formally notified the International Atomic Energy Agency of its agreement to the nuclear fuel swap deal, under which it would ship some low-enriched uranium to Turkey in return for higher-grade fuel for a Tehran research reactor.

Western governments have been dismissive of the deal, arguing that the international community needs to keep up the pressure on Tehran to heed U.N. Security Council demands over its nuclear program.

Brazil and Turkey had written letters to the leaders of the United States, France, Russia and Mexico, stressing the importance of the nuclear fuel swap agreement and saying it indicated Iran's readiness for dialogue.

Iran is already under three sets of U.N. sanctions over its refusal to suspend the sensitive process, which lies at the center of Western fears that the program is cover for a drive for a nuclear weapon. Iran denies any such ambition.