The visit of Olli Heinonen, deputy director general of the International Atomic Energy Agency (IAEA), follows his talks with Iranian officials in the capital of the Islamic Republic on August 7-8. Iranian officials described the talks as "constructive."
The parties did not give any details of the talks, but analysts said the new round of negotiations were likely to focus on Iran's nuclear research activities.
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.
Tehran has so far ruled out the suspension of uranium enrichment, which would trigger formal negotiations on an enhanced package of incentives proposed by the so-called Iran Six - the world powers involved in nuclear negotiations with the Islamic Republic. 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 Iran Six - the U.S., Britain, China, Russia, Germany, and France - have pledged to stop further UN sanctions in return for Iran freezing its nuclear program.
In a report on Iran in late May, the IAEA Director General Mohamed ElBaradei said the country's alleged studies into developing nuclear warheads remained a matter of serious concern, and that Tehran must provide more information on its "missile-related activities".
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 resolve the dispute.
