The latest violation of the deal aimed at preventing Tehran from developing nuclear weapons comes days after US President Joe Biden made clear he would not lift sanctions against Iran unless it first adheres to agreement's commitments.

The Vienna-based International Atomic Energy Agency (IAEA) said in a statement seen by AFP that on February 8 it "verified 3.6 grammes of uranium metal at Iran's Fuel Plate Fabrication Plant in Esfahan".

IAEA director general Rafael Grossi informed member states of the new violation, the statement added.

Iran has previously said its research on uranium metal production was aimed at providing advanced fuel for a research reactor in Tehran.

But the topic is sensitive because uranium metal can be used as a component in nuclear weapons.

The deal says that after 10 years Iran would have been allowed to initiate research on producing uranium metal-based fuel "in small agreed quantities" but only if the other parties -- the US, China, Russia, Germany, France and Britain -- had given approval.

The new violation comes a month after Iran announced it had stepped up its uranium enrichment process to 20 percent purity, far above the 3.67 percent level permitted by the deal, but far below the amount required for an atomic bomb.

In 2018 US President Donald Trump dramatically withdrew from the Iran nuclear deal and reimposed crippling economic sanctions on Tehran. The following year Tehran announced it would start breaking the deal's limits on nuclear activity.

Trump's successor Biden is seeking to revive the agreement, but the two sides appear to be in a standoff over who acts first.

"If they want Iran to return to its commitments... the United States must entirely lift the sanctions, in practice and not on paper," supreme Iranian leader Ali Khamenei said Sunday.

When Biden was asked on Sunday whether he would halt sanctions to convince Iran to return to the bargaining table, Biden offered a clear reply: "No."