The acting head of the UN atomic watchdog, Cornel Feruta, arrived in Tehran on Sept.8 for high-level talks with Iranian officials, the semi-official ISNA news agency reported.
The International Atomic Energy Agency official's visit comes a day after Iran announced its latest step in reducing its commitments to a 2015 nuclear deal.
The Romanian diplomat was to meet Iran's Atomic Energy Organisation chief Ali Akbar Salehi, Foreign Minister Mohammad Javad Zarif, and Ali Shamkhani, secretary of Iran's Supreme National Security Council, ISNA said.
The IAEA said the visit was part of its "ongoing interactions" with Tehran, including "verification and monitoring in Iran under the Joint Comprehensive Plan of Action (JCPOA)," the technical name for the 2015 deal.
The accord gave Iran relief from sanctions in return for curbs on its nuclear programme.
Iran's Atomic Energy Organisation said on Sept.7 that it had fired up 20 IR-4 and 20 IR-6 advanced centrifuges -- a third step it has taken back from the nuclear deal.
Despite the latest move, the agency said Iran would allow the IAEA to continue monitoring its nuclear facilities in accordance with the 2015 agreement.
In response, the IAEA said it had noted Iran's latest move and indicated its inspectors were ready to check its compliance.
"Agency inspectors are on the ground in Iran and they will report any relevant activities to IAEA headquarters in Vienna," spokesman Fredrik Dahl said.
Iran has taken a series of retaliatory steps to reduce compliance with the deal after the United States withdrew from it last year and began reimposing sanctions against the Islamic republic.
On July 1, Iran said it had increased its stockpile of enriched uranium to beyond the 300-kilogramme limit set by the agreement.
A week later, it announced it had exceeded the deal's uranium enrichment limit of 3.67 per cent.
Feruta's visit to Tehran comes a day before the IAEA board of governors convenes for a quarterly meeting in Vienna, at which its verification and monitoring mission in Iran will be discussed.
In its latest report on August 30, the watchdog said it was continuing to verify compliance through cameras and on-site inspections.
But in an apparent hint at worries about access, it said "ongoing interactions... require full and timely cooperation by Iran".
