Representatives of international organizations invited to Iran arrived in central city of Natanz to tour nuclear facilities, ISNA reported.
The delegation arrived in Iran on Saturday dawn visited Iran's 40-megawatt heavy water reactor installations in central city of Arak on Saturday.
Representatives and presidents of Non-Aligned Movement (NAM) troika which includes Iran, Egypt and Cuba, Group of 77, the Arab League and Venezuelan and Syrian ambassadors to the International Atomic Energy Agency (IAEA) are the guests.
Natanz enrichment facilities can enrich uranium fuel by 20 percent.
The delegation is to return to Tehran after visiting the nuclear installations and meet with Iranian Supreme National Security Council Secretary Saeed Jalili ahead of leaving for Vienna on Monday dawn.
Senior officials including Atomic Energy Organization of Iran (AEOI) Chief Ali Akbar Salehi and Foreign Ministry Spokesman Ramin Mehmanparast have already said that Iran's invitations to its nuclear sites show its good will and transparent nuclear activities.