Iran said Wednesday it would "automatically" return to its nuclear commitments if US President-elect Joe Biden lifts sanctions, as the outgoing administration doubled down with more pressure.

Biden has promised a return to diplomacy with Iran after four hawkish years under Donald Trump, who withdrew from a denuclearisation accord and slapped sweeping sanctions.

Tehran again meeting its commitments "can be done automatically and needs no conditions or even negotiations," Foreign Minister Mohammad Javad Zarif said in comments published in the state-run Iran daily.

Zarif described Biden as a "foreign affairs veteran" whom he has known for 30 years. Once in the White House, Biden could "lift all of these (sanctions) with three executive orders," Zarif argued.

If Biden's administration does so, Iran's return to nuclear commitments will be "quick", the minister added.

Washington's return to the deal, however, could wait, Zarif added.

"The next stage that will need negotiating is America's return... which is not a priority," he said, adding that "the first priority is America ending its law-breaking".

President Hassan Rouhani meanwhile called the Trump administration "unruly", and said a Biden administration could "bring back the atmosphere" that prevailed in 2015 at the time of the nuclear deal, negotiated by Barack Obama's administration in which Biden was vice president.

The accord offered Tehran relief from international sanctions in exchange for guarantees, verified by the United Nations, that its nuclear programme has no military aims.

 - Trump team doubles down -

 Trump, who has not accepted defeat in the November 3 election, is moving to keep ramping up pressure on Iran, hoping to make it more difficult politically and legally for Biden to ease sanctions.

In the latest moves, the Treasury Department said it was freezing any US interests of the Foundation of the Oppressed, officially a charitable organisation for the poor that has interests across the Iranian economy.

The Treasury described the foundation as a "multibillion-dollar economic empire" and "key patronage network" for Iran's supreme leader Ayatollah Ali Khamenei that operates without government oversight.

Also hit by sanctions was Iran's minister for intelligence and security, Mahmoud Alavi, on human rights grounds.

Outgoing Secretary of State Mike Pompeo, in an indirect response to Zarif as he arrived in US ally Israel, vowed to keep imposing "painful consequences".

"The Iranian regime seeks a repeat of the failed experiment that lifted sanctions and shipped them huge amounts of cash in exchange for modest nuclear limitations," he said.

"This is indeed troubling, but even more disturbing is the notion that the United States should fall victim to this nuclear extortion and abandon our sanctions."

Iran, which denies it is seeking to build a nuclear bomb, has since May 2019 gradually suspended most of its key obligations under the agreement, including limits to the production and stockpiling of low-enriched uranium.

The UN's International Atomic Energy Agency said Wednesday Iran had begun operating advanced centrifuges at an underground section of its primary nuclear enrichment facility at Natanz.

Under Iran's deal with world powers, it is only meant to enrich uranium with a less sophisticated variety of centrifuges.

In its report last week the IAEA said Iran's stockpile of enriched uranium now stood at over 12 times the limit in the 2015 accord.

The New York Times reported Monday that Trump had last week asked top aides about the possibility of striking Iran's nuclear facilities.

Senior officials reportedly "dissuaded the president from moving ahead with a military strike," warning him such an attack could escalate into a broader conflict in the last weeks of his presidency.

Iran argues it has moved away from its commitments because of the sanctions and the inability of the other parties -- Britain, China, France, Germany and Russia -- to provide it with the deal's promised economic benefits.