"The minister is scheduled to have a short working visit today in Iran," said Russian foreign ministry spokesman Mikhail Kamynin, quoted by the Interfax news agency.

"He will examine a series of subjects linked to the situation of the Iranian nuclear programme and questions concerning bilateral relations," he added. Lavrov was due to arrive later in the afternoon from Kazakhstan.

The trip comes just two weeks after a landmark visit Iran by Russian President Vladimir Putin, the first by a Kremlin chief since World War II.

Putin has in recent weeks been increasingly critical of US moves for more UN sanctions and unilateral sanctions as well as Washington's refusal to rule out military action against Tehran over its nuclear programme.

"Why make the situation worse, bring it to a dead end, threaten sanctions or even military action," he said last Thursday ahead of an EU-Russia summit in Lisbon.

"You can run around like mad people wielding razor blades but it is not the best way to resolve the problem."

Some Iranian officials said after Putin's visit that he made a proposal over the Iranian nuclear programme to supreme leader Ayatollah Ali Khamenei. However this was never confirmed by Moscow.

The United States and its European allies accuse Iran of seeking a nuclear bomb and are threatening a third set of UN sanctions against Tehran to punish its nuclear defiance.

However Russia, a veto-wielding permanent UN Security Council member which has close economic ties with Tehran, has repeatedly expressed doubt over the Western claims that Iran's nuclear drive has military aims.

China also issued an unusually blunt statement saying it remained opposed to further sanctions against Iran and insisted diplomacy was the best way to resolve the issue.

"Under the current circumstances we do not support further sanctions, as that would worsen the situation," foreign ministry spokesman Liu Jianchao told reporters.

The White House has recently ramped up its rhetoric against Iran, warning the world about "nuclear holocaust" and "World War III" if Tehran obtained atomic weapons.

Ahmadinejad, who is due to meet Lavrov at 1630 GMT, on Tuesday reaffirmed that Iran would never give in to the chief Western demand over its nuclear drive -- that it suspends uranium enrichment.

"All the plans to stop the Iranian people have failed and the enemies know that they cannot prevent the progress of Iran."

Putin's lightning one-day visit to Tehran for a summit of Caspian Sea heads of state was hailed by Iran as a major diplomatic success.

He backed the Iranian nuclear programme and spoke out against the use of force, much to the delight of his hosts. State media quoted him as telling Khamenei his visit had opened up a "new page" in relations.

But a shadow was cast by his refusal to commit to a concrete date for the completion of Iran's first nuclear power plant, a much delayed project that a Russian contractor is building in the southern city of Bushehr.

Meanwhile, a UN nuclear agency delegation headed by deputy director general Olli Heinonen was holding a second day of talks with Iranian officials in Tehran on Iran's use of uranium-enriching centrifuges.

The talks are part of a deal Heinonen clinched in August for Iran to answer outstanding questions over its atomic programme but the accord has been bitterly criticised by the United States for not going far enough.

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