Yukiya Amano, Director General of the U.N. International Atomic Energy Agency (IAEA), said that he planned to meet with Iran's Foreign Minister Ali Akbar Salehi next week, but had no firm details yet, Reuters reported.
The UN nuclear chief told that he was "quite concerned" over plans by Tehran to triple uranium production capacity.
"The most important message for Iran is that they need to fully implement the safeguard agreement and other relevant obligations. Further cooperation is needed to restore the confidence of the international community," he said.
"We are quite concerned about that," Amano said, confirming that the IAEA had received a "very simple" letter from Iran about the plans.
Amano reiterated he would consider accepting an invitation to visit Iran but stressed it would have to yield concrete results: "For now I don't see, unfortunately, progress."
Iran announced last month it would shift its production of higher-grade uranium to an underground bunker and triple output capacity in a defiant move that further fueled Western unease about Tehran's intentions.
Western powers suspect Iran is seeking to develop a nuclear weapons capability while Tehran rejects the charge, saying its nuclear program is aimed at generating electricity.
Iran's refusal to halt enrichment has led to four rounds of U.N. sanctions on the major oil producer, as well tighter U.S. and European Union restrictions.