US President Donald Trump has restored his “maximum pressure” campaign on Iran that includes efforts to halt its oil exports to prevent Tehran from obtaining a nuclear weapon.

Ahead of his meeting with Israeli Prime Minister Benjamin Netanyahu, Trump signed a presidential memorandum reimposing Washington’s tough policy on Iran from his first term.

As he signed the memo, Trump described it as very tough and said he was torn on whether to do so. He said Iran could not have nuclear weapons and he hoped a deal could be reached with Tehran.

Trump has accused former US president Joe Biden of failing to rigorously enforce oil-export sanctions. He says that emboldened Tehran by allowing it to sell oil to fund a nuclear weapons program and armed militias in the Middle East.

Iran is “dramatically” accelerating enrichment of uranium to up to 60 per cent purity, close to the roughly 90 per cent weapons-grade level, the UN nuclear watchdog chief told Reuters in December. Iran has denied wanting to develop a nuclear weapon.

Trump’s memo, among other things, orders the US Treasury secretary to impose “maximum economic pressure” on Iran, including sanctions and enforcement mechanisms on those violating existing sanctions.

It also directs the US Treasury and State Department to implement a campaign aimed at “driving Iran’s oil exports to zero”.

US oil prices fell on Tuesday (local time) on the news that Trump planned to sign the memo, which offset some weakness from the tariff drama between Washington and Beijing.

Iran’s mission to the United Nations in New York did not immediately respond to a request for comment.

Tehran’s oil exports brought in $US53 billion ($A86 billion) in 2023 and $US54 billion ($A88 billion) a year earlier, according to US Energy Information Administration estimates. Output in 2024 was running at its highest level since 2018, based on OPEC data.

Trump had driven Iran’s oil exports to near-zero during part of his first term after re-imposing sanctions. They rose under Biden’s tenure as Iran succeeded in evading sanctions.

China does not recognise US sanctions and Chinese businesses buy the most Iranian oil. China and Iran have also built a trading system that uses mostly Chinese yuan and a network of middlemen, avoiding the dollar and exposure to US regulators.

Trump also directed his UN ambassador to work with allies to “complete the snapback of international sanctions and restrictions on Iran”, under a 2015 deal between Iran and key world powers that lifted sanctions on Tehran in return for restrictions on its nuclear program.

The US quit the agreement in 2018, during Trump’s first term, and Iran began moving away from its nuclear-related commitments under the deal. The Trump administration had also tried to trigger a snapback of sanctions under the deal in 2020, but the move was dismissed by the UN Security Council.

Britain, France and Germany told the UN Security Council in December that they were ready – if necessary – to trigger a return to all international sanctions to prevent Iran from acquiring a nuclear weapon.

They will lose the ability to take such action on October 18 when a 2015 UN resolution expires. The resolution enshrines Iran’s deal with Britain, Germany, France, the US, Russia and China that lifted sanctions on Tehran in exchange for restrictions on its nuclear program.

-AAP