Rafael Grossi, who on Monday was formally appointed to a second four-year term as head of the International Atomic Energy Agency, said talks between the UN body and Tehran “have not made the progress I was hoping for”.
Iran told the IAEA’s annual conference in Vienna that the country's co-operation should not be “taken as granted”, as it insisted the aims of its nuclear programme were peaceful.
Tehran agreed to curbs on its nuclear activities in exchange for sanctions relief as part of a deal with global powers in 2015. The US pulled out of the agreement in 2018 and Iran has since increased uranium enrichment.
In a message read out to the conference, UN Secretary General Antonio Guterres said the Iran deal “remains vital to the global nuclear non-proliferation architecture and to regional and international security”.
The IAEA has an “essential role in impartially and expertly monitoring” that the terms of the agreement are upheld, while “seeking sustainable solutions to the outstanding issues regarding Iran’s nuclear programme”, Mr Guterres said.
Attempts to revive the deal have failed and Britain, France and Germany announced this month they would extend sanctions on Iran that were due to expire in October under the original agreement.
The IAEA is also in a separate dispute with Iran over unexplained traces of uranium in the country.
Mr Grossi said the agency could not verify whether Tehran’s activities were peaceful until it received a satisfactory explanation for the material.
He is “ready to work with Iran” on matters related to the "de facto suspended implementation" of the 2015 deal, he said.
He said the IAEA was still "actively engaged" despite talks falling short after he visited Tehran in March.
“Only full co-operation by Iran, and tangible results, will take us to the credible assurances that Iran’s nuclear programme is exclusively peaceful,” Mr Grossi told the conference.
The head of the Iran’s atomic energy agency, Mohammad Eslami, said the country was determined to expand its use of nuclear power in civilian projects despite the doubts over its intentions.
He said it was “baseless and unacceptable” for US sanctions to remain in place for breaches of the 2015 deal.
Iran “once again asserts that the present extensive co-operation with the IAEA should not be taken as granted and should not be negatively affected by following short-sighted political agendas”, he said.
Western powers have said Iran’s enrichment of uranium to 60 per cent has no credible civilian purpose. The original deal with the US, Britain, France, Germany, Russia and China set a cap of 3.67 per cent.
However, those countries have stopped short of invoking a “snapback” that would reset the clock to when UN sanctions were in place before 2015. The option to do that expires in 2025.
On the same date, the UN Security Council “will have concluded its consideration of the Iranian nuclear issue” unless a snapback is put in place before then.