The International Atomic Energy Agency (IAEA) has since 2021 been struggling to monitor Iran's nuclear programme, which Tehran has stepped up, denying that it seeks to build a bomb.

"We have to deploy every effort... to prevent a country that has capabilities which could potentially lead to the development of nuclear weapons from doing it," Rafael Grossi told a US State Department non-proliferation conference in a recorded video message.

"We saw the failure of this type in the Democratic People's Republic of Korea, North Korea", which conducted its first nuclear test in 2006 despite diplomatic efforts, he said in a speech seen on Tuesday by AFP.

Inspectors from the IAEA were kicked out of North Korea in 2009, and the agency has since monitored it from outside, including through commercial satellite imagery.

The "uncertainties and dangers on the Korean peninsula and in Asia" have since increased, Grossi said.

"This is why our current efforts in Iran are so fundamental, and... why the support of the international community and of course the United States is indispensable for us," he added.

"The IAEA is the eyes and ears and presence of the international community in Iran," he said.

In 2015, major world powers reached a deal with Iran, under which Tehran would curb its nuclear programme in exchange for relief from crippling economic sanctions.

That started to unravel in 2018 when then US president Donald Trump unilaterally withdrew from it and reimposed sanctions.

Efforts to revive the deal have so far been fruitless.

In September, Grossi said he was concerned the international community was losing interest in holding Iran to account over its advancing nuclear programme.

Iran then withdrew the accreditation of eight top inspectors.

In its latest reports, the UN nuclear watchdog deplored that Iran had made "no progress" on several outstanding nuclear issues.

These include reinstalling several IAEA monitoring cameras Tehran had removed from its nuclear sites and explaining the presence of uranium particles found in Iran.