International Atomic Energy Agency director general Rafael Grossi made the comments ahead of a meeting in Cairo with Iran's top diplomat and chief nuclear negotiator, Abbas Araghchi.

It comes a day after a leaked IAEA report showed Iran has stepped up production of uranium enriched up to 60 percent -- close to the roughly 90 percent level needed for atomic weapons.

In a joint press conference with Egyptian Foreign Minister Badr Abdelatty before the scheduled tripartite meeting, Grossi defended the report, calling it "impartial".

"We say things as they are without a political agenda," Grossi said, stressing the report "tells it as it is".

"There is a need for more transparency -- this is very, very clear -- in Iran, and nothing will bring us to this confidence (besides) full explanations of a number of activities," he added.

Iran has rejected the IAEA's findings, calling it a "political" manouevre based on "unreliable and misleading information".

Grossi said some of the report's findings "may be uncomfortable for some, and we are... used to being criticised".

In a phone call with Grossi on Saturday, Araghchi warned Iran would retaliate if European powers that have threatened to reimpose nuclear sanctions "exploit" the report.

Abdelatty urged a peaceful solution, saying "the region is already experiencing enough crises and security challenges".

"We completely reject any escalation or incitement of a military option," he said, warning against "descending into a state of chaos from which no one will be spared".

The UN report comes as Iran holds talks with the United States on its nuclear programme, after Washington unilaterally abandoned a landmark agreement between Tehran and world powers in 2018 during President Donald Trump's first term.

Iran on Monday demanded a US guarantee that sanctions will be lifted as part of a nuclear deal.

The 2015 deal aimed to stop Iran from developing a nuclear bomb -- a goal Western countries accused it of pursuing, though Tehran denies it.

The Iranian foreign minister said Saturday he had received "elements" of a US proposal for a potential nuclear deal following five rounds of Omani-mediated talks.

The UN agency's board of governors is set to review Iran's nuclear activities in its upcoming quarterly meeting in Vienna starting June 9.