The United States on Wednesday called on Iran to dilute all of the uranium it has enriched to up to 60% purity, close to the weapons-grade level of roughly 90%, Reuters reported.

The US statement comes after the International Atomic Energy Agency (IAEA) said in a report last week that Iran's stock of uranium enriched to up to 60% had fallen slightly in the past quarter as it had diluted, or "downblended", more of its most highly enriched material than it had produced.

The report stressed that Iran still has enough of that material, if enriched further, to fuel two nuclear weapons and enough for more bombs at lower enrichment levels.

"Iran should downblend all, not just some, of its 60% stockpile, and stop all production of uranium enriched to 60% entirely," the United States said in a statement on Iran to a quarterly meeting of the 35-nation IAEA Board of Governors, according to Reuters.

"We continue to have serious concerns related to the stockpile of highly enriched uranium that Iran continues to maintain," the US statement added.

"No other country today is producing uranium enriched to 60% for the purpose Iran claims and Iran's actions are counter to the behavior of all other non-nuclear weapons states party to the NPT (Non-Proliferation Treaty)," it concluded.

Between June and November last year, Iran slowed down the enrichment to 3 kg per month, but jumped back up to a rate of 9 kg at the end of the year, the IAEA previously reported.

The increase came soon after Tehran barred a third of the IAEA's core inspections team, including the most experienced, from taking part in agreed monitoring of the enrichment process.

Under the original nuclear deal with world powers in 2015, Iran was allowed to enrich uranium only up to 3.67% purity, maintain a stockpile of uranium of 300 kilograms, and use only very basic IR-1 centrifuges, machines that spin uranium gas at high speed for enrichment purposes, in exchange for the lifting of economic sanctions.

However, Iran has scaled back its compliance with the 2015 deal in response to former President Donald Trump’s withdrawal from the agreement in 2018.

The Biden administration sought to return to the deal and held indirect talks with Iran on a return to compliance, but the negotiations reached a stalemate last September, after Iran submitted a response to a European Union proposal to revive the deal.

The IAEA reports last week were published several days after the agency’s director-general, Rafael Grossi, said that Iran continues to enrich uranium well beyond the needs for commercial nuclear use despite UN pressure to stop it.

He also pointed out concerns over the fact that senior officials in Iran have recently said they have all the elements for a nuclear weapon.