Nuclear inspectors from the United Nations begin a three-day visit to Iran today.
The team of experts from the International Atomic Energy Agency (IAEA) are not expected to visit any nuclear facilities but will hold talks with Iranian officials.
The head of the IAEA team, Herman Nackaerts, urged Iran to work with the mission, adding such cooperation is long overdue.
An IAEA report in November said some of Iran's nuclear activities can have no other purpose than developing nuclear weapons, a charge Iran regularly denies.
Earlier this month, the IAEA said Iran had begun enriching uranium to 20 percent purity inside a mountain bunker at Fordow.
Reports out of Iran said the IAEA might visit Fordow during the current visit, but IAEA diplomats in Vienna have denied such reports.
UN Secretary-General Ban Ki-moon says the onus is on Iran to prove its nuclear program is peaceful.
Iran has been subjected to four rounds of UN sanctions for failing to halt uranium enrichment until the IAEA can clear up questions about its nuclear program.
Iranian nuclear officials say Tehran hopes the mission will clear up "ambiguities" over Iran's nuclear program.
Iran ended full cooperation with the IAEA in 2008.
Officials at the IAEA say their team -- which includes two senior weapons experts -- will be hoping to talk to key Iranian scientists suspected of weapons work as well as inspect documents relating to such suspected work.
Analysts say the IAEA hopes the visit will help lead to a resumption of six-party international talks on Iran's nuclear program.
The latest round of such talks last January in Istanbul ended with no breakthrough.
Compiled from agency reports