The visit of Olli Heinonen, deputy director general of the International Atomic Energy Agency (IAEA), comes a day after the 'Iran Six' negotiating countries agreed to consider new sanctions against the Islamic Republic for its refusal to halt uranium enrichment.
"The two sides will assess the trend of cooperation between the Iranian Atomic Energy Organization and the IAEA," official news agency IRNA said.
At talks with Iran in Geneva on July 19, the six nations - China, Russia, the U.S., France, Britain and Germany - put forward a package of trade and nuclear technology incentives, demanding a response from Tehran within two weeks.
European Union foreign policy chief Javier Solana received on Tuesday a letter from Tehran, which he said did not contain a clear response to the proposals.
The Iranian media said Heinonen would not discuss the situation around the proposals but focus on 'technical' issues of cooperation between Tehran and the IAEA during talks with the deputy head of Iran's Atomic Energy Organization, Mohammad Saidi, and Iran's envoy to the IAEA, Ali Asghar Soltanieh.
Heinonen last visited Iran in April-May in an attempt to clarify outstanding questions the IAEA has about Iran's nuclear program, especially issues relating to Tehran's past research into making a nuclear warhead.
Iran has repeatedly dismissed Western suspicions that it is seeking to build nuclear weapons under the guise of a civilian nuclear program. The Islamic Republic has also consistently insisted on its right to peaceful nuclear research.
However, in a report on Iran in late May, the IAEA Director General Mohamed ElBaradei said the country's alleged studies into making nuclear warheads remained a matter of serious concern, and that Tehran must provide more information on its "missile-related activities".
According to the UN nuclear watchdog, there has been no progress on the issue since then.
Iran is currently under three sets of relatively mild UN Security Council sanctions for defying demands to halt uranium enrichment, which it says it needs purely for electricity generation.
The U.S. and Israel have refused to rule out military action against Iran, the world's fourth largest oil producer, if diplomacy fails to end the dispute.
The Russian Foreign Ministry said on Wednesday that the Iran Six would continue attempts to resolve the dispute over Tehran's nuclear program by diplomatic means.
