Experts from the UN's nuclear watchdog are due to hold talks in Tehran on October 7 over outstanding issues regarding Iran's atomic program.
The visit by International Atomic Energy Agency (IAEA) Deputy Director-General Tero Varjoranta and a delegation comes as the agency seeks to learn whether Iran's nuclear activities have had military aspects.
Iran failed to meet an August 25 deadline for providing information requested by the IAEA regarding the issue.
Separately, Russian Deputy Foreign Minister Sergei Ryabkov said in Moscow on October 6 that he believes Tehran and six world powers can reach a final deal over Iran's nuclear program by their deadline of November 24.
In Brussels, Federica Mogherini, the European Union's commissioner-designate for foreign policy, said that if an agreement cannot be reached by November 24, "it will be extremely complicated to get one afterward."