Olli Heinonen, deputy director general of the International Atomic Energy Agency, is continuing his meetings with the Islamic Republic's top security and nuclear officials behind closed doors at Iran's Atomic Energy Organization (IAEO).
As was reported previously, he will address Iran's "purported nuclear research."
The state news agency IRNA said on Monday that Heinonen had met with Ali Asghar Soltanieh, Iran's permanent representative to the IAEA.
IAEO Deputy Head for International affairs Mohammad Saeedi along with Soltaniyeh was also present at the talks. The Iranian delegation is headed by Javad Vaeedi, deputy head of the Supreme National Security Council (SNSC) for international affairs.
Hermann Nackartes, a regional head at the UN nuclear watchdog is accompanying Heinonen on his Tehran visit.
An informed source told IRNA that the IAEA delegation will not carry out any inspections of Iran's nuclear facilities and that they would leave Tehran following talks with Iranian officials on Wednesday.
The IAEA said in a report released in late February that Iran had become more transparent on its nuclear program, but had failed to fully answer allegations relating to nuclear weapons development.
The international community has demanded that Tehran halt uranium enrichment, used both in electricity generation and nuclear weapons production. Iran insists on its right to civilian nuclear energy, and has defied three sets of United Nations sanctions over its nuclear program.
In a sign of defiance Iran said earlier this month it had started to install another 6,000 uranium enrichment centrifuges at its underground facility in Natanz in addition to its 3,000. The country also announced tests of advanced enrichment centrifuges, along with plans to build a second uranium processing plant by next March.
The country's nuclear ambitions have fueled tensions with Washington, with U.S. President George Bush refusing late last year to rule out military action against Tehran.
Russia and China, which both have strong business interests in Iran, blocked stronger measures against the country using their vetoes at the UN Security Council.