He called for a cessation of hostilities.

The request follows attacks by Israel and the United States on Iran's nuclear facilities.

"Iran, Israel and the Middle East need peace," Rafael Grossi, director of the International Atomic Energy Agency (IAEA), told an emergency meeting of the organisation's board of governors in Vienna.

"For that, we must take a number of steps," he said.

"First of all, we must return to the negotiating table and for that allow IAEA inspectors -- the guardians on our behalf of the NPT (nuclear non-proliferation treaty) -- to go back to Iran's nuclear sites and account for the stockpiles of uranium, including, most importantly, the 400 kilogrammes enriched to 60 percent."

Grossi said Tehran had sent him a letter on June 13 announcing the implementation of "special measures to protect nuclear equipment and materials".

"There needs to be a cessation of hostilities for the necessary safety and security conditions to prevail so that Iran can let IAEA teams into the sites to assess the situation," he said.

Over the weekend, the United States struck three Iranian nuclear sites, joining Israel's bombardments of Iran's nuclear programme.

"Craters are now visible at the Fordo site, Iran's main facility for enriching uranium at 60 percent, indicating the use of ground-penetrating munitions," he said.

He added that "very significant damage" is expected to have occurred for the US bombing "given the explosive payload utilised and the extreme vibration-sensitive nature of centrifuges".

"At this time, no-one including the IAEA, is in a position to have fully assessed the underground damage at Fordo," he said.

The US strikes came after Israel began launching large-scale attacks on Iran on June 13 targeting its missile and nuclear facilities, military leaders and security services, and residential sites.

Iran's uranium enrichment has for decades caused tension, with Western powers voicing fears the drive is aimed at making an atomic bomb, a claim denied by Tehran.

Israel has maintained ambiguity about its own atomic arsenal, neither officially confirming nor denying it exists, but the Stockholm International Peace Research Institute has estimated it has 90 nuclear warheads.

European powers have urged Tehran to revive diplomatic efforts with the United States to find a solution in the standoff over its nuclear programme.

Iran has said it can only consider diplomacy once Israel halts its bombardment of the Islamic republic.