By Sadeq Saba
BBC regional analyst
Russia has urged Iran to suspend its uranium enrichment programme in order to avoid possible sanctions from the UN Security Council.
Moscow say it wants to press ahead with its co-operation
Russian Foreign Minister Sergei Lavrov said Moscow would continue nuclear co-operation with Tehran if it complies with the UN nuclear agency (IAEA).
In its meeting last month, the IAEA called on Iran to suspend its nuclear fuel cycle.
The US accuses Iran of secretly trying to develop nuclear weapons.
The Russian foreign minister's visit to Tehran is widely seen as a mission to convince Iran to suspend its uranium enrichment programme as required by the IAEA.
Russia has been helping Iran to build its first nuclear power plant in the southern port of Bushehr.
Despite increasing pressure from Washington to abandon the project, Moscow has insisted that it is determined to press ahead with its nuclear co-operation with the Islamic Republic.
But Russia is now concerned that if Tehran does not comply with the IAEA's ultimatum to suspend the uranium enrichment activities by the end of November, Iran could be referred to the UN Security Council for possible sanctions.
At his press conference in Tehran, Mr Lavrov said Moscow was against such a measure. Any sanctions against Iran would threaten the $800m (£445m) Bushehr deal.
Russia is also keen to continue its lucrative economic relations with Iran, a key partner for Moscow in the region. It is believed that if Mr Lavrov's mission to Tehran is successful, Mr Putin may visit the country afterwards.
Construction of the Bushehr power plant has been severely delayed for other reasons. But now the Russian foreign minister and his Iranian counterpart say their countries are close to signing a deal on the supply and return of nuclear fuel for the plant.