Iran's supreme leader Ayatollah Ali Khamenei said Sunday the US must "completely lift" sanctions first, followed by verification by Tehran, before the Islamic republic returns to its nuclear deal commitments.

"If they want Iran to return to its commitments ... America must completely lift sanctions, and not just in words or on paper," Khamenei said in a televised speech to air force commanders.

"They must be lifted in action, and then we will verify and see if they have been properly lifted, and then return," he added.

The 2015 landmark deal has been hanging by a thread since US President Donald Trump's decision to withdraw from it in 2018 and reimpose sanctions on Tehran.

Tehran a year later suspended its compliance with most key nuclear commitments to the deal.

The new administration of US President Joe Biden has expressed willingness to return to the deal, but insisted that Tehran first resume full compliance.

On January 4, Iran announced it has 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.

And it may restrict by February 21 nuclear inspections if US sanctions are not lifted or other key parties to the deal do not help Tehran bypass them, according to a law passed by the parliament in December.

According to Khamenei, Iran has "a right to set conditions for the continuation" of the deal as it has upheld its end, unlike the US and the three European members of the deal -- Britain, France and Germany -- who have "violated all their commitments".

"No one in the Islamic republic cares for the nonsense claimed by those not entitled to anything," he said.

Khamenei insisted that the condition set by Tehran for the US is Iran's "definite policy".

Iran "will not turn back from" it, he said.

On Monday, Iranian Foreign Minister Mohammed Javad Zarif asked the European Union to coordinate a synchronised return of both Washington and Tehran into a nuclear deal, after a diplomatic standoff on who will act first.