Russian Foreign Minister Sergey Lavrov told his Iranian counterpart Saturday that Tehran must halt its uranium enrichment activity and work with the U.N. nuclear watchdog to answer questions about its nuclear program.

The Foreign Ministry said the demand was made in a telephone phone conversation between Lavrov and Iranian Foreign Minister Manouchehr Mottaki.

Lavrov "emphasized the urgent necessity for Iran to take concrete steps aimed at restoring confidence on the part of the international community about its nuclear activity, including the suspension of R&D (research and development) work on uranium enrichment," the Foreign Ministry said in a statement.

He also demanded that Iran "provide full-format cooperation" with the International Atomic Energy Agency to "clear up the IAEA's remaining questions" about its nuclear program.

The phone call, which the ministry said was initiated by the Iranian side, came amid a mounting standoff over Tehran's nuclear activities, which the United States and other nations believe are aimed at creating nuclear weapons.

Lavrov's statement, which was strongly worded but repeated earlier calls on Iran to halt enrichment and cooperate with the IAEA, came a day after a new report by the agency confirmed that Tehran refused to comply with a U.N. Security Council demand that it halt enrichment by a Friday deadline.

With the Security Council expected to begin debating new steps next week aimed at persuading Iran to knuckle under, Lavrov's demands marked a last-ditch attempt to sway Tehran and avert the possibility of a council vote on measures that could include a threat of sanctions, which Russia opposes.

It also appeared aimed to indicate to other nations that Russia — while opposing sanctions or the use of military force and insisting that the IAEA, not the Security Council, take the lead in efforts to resolve the standoff — is not coddling Iran.

Moscow has close ties to Iran and is building the nation's first nuclear power plant, but has been frustrated by Tehran's defiance of the international pressure and its refusal to adopt a Russian proposal aimed at easing tension by moving Iran's uranium enrichment to Russian territory.