UNITED NATIONS — A showdown looms at the United Nations over Iran on Tuesday as President Donald Trump and Iranian leader Hassan Rouhani are set to square off during the world’s biggest diplomatic gathering.

On the opening day of the General Assembly debate, Trump and Rouhani are to take their turn at the podium four months after the US president ditched the Iran nuclear deal.

The five remaining parties to the agreement – Britain, China, France, Germany and Russia – announced on Monday plans to keep business ties alive with Iran, staring down Washington’s move to impose sanctions.

Eyeing his second summit with North Korean leader Kim Jong Un, Trump will also tout his diplomacy with Pyongyang as a win, even if the North has taken little concrete action to dismantle its missile and nuclear programs.

Trump withdrew from the nuclear deal in May, to the dismay of European allies, Russia and China which had invested years in negotiations to achieve a milestone agreement on keeping Iran’s nuclear ambitions in check.

In his address, Rouhani will stress that Iran continues to stick to the 2015 deal and portray the United States as a pariah for breaking its international commitments.

Trump used his UN address last year to bash the nuclear deal as "an embarrassment", signaling that the United States was ready to walk away from the agreement.

After its exit, the United States maintains that it is seeking to ramp up pressure on Iran which it accuses of sowing chaos in Iraq, Syria, Yemen and Lebanon.

"As I have said repeatedly, regime change in Iran is not the administration’s policy," Trump’s national security adviser John Bolton told reporters.

"We’ve imposed very stringent sanctions on Iran, more are coming, and what we expect from Iran is massive changes in their behavior," he said.

After a late meeting on Monday, EU foreign policy chief Federica Mogherini announced that a new legal entity would be set up to preserve oil and other business links with Iran.

"This will mean that EU member-states will set up a legal entity to facilitate legitimate financial transactions with Iran and this will allow European companies to continue to trade with Iran," Mogherini told reporters, flanked by Iranian Foreign Minister Mohammad Javad Zarif.

No Trump-Rouhani meeting

Rouhani has said he has no plans to meet Trump while in New York during the marathon of meetings and slammed the offer of talks as "not genuine".

As a precondition for any dialogue, Rouhani said Trump would need to repair the damage done by exiting the nuclear deal. "That bridge must be rebuilt," he told NBC news.

On Wednesday, Trump will for the first time chair a meeting of the Security Council on non-proliferation that will give him a fresh opportunity to make the case for a tougher international stance on Iran.

"The Trump administration’s approach toward Iran seems to boil down to: squeeze and let’s see what will come," said Robert Malley, president of International Crisis Group.

Malley warns that "rising tensions between the US and Iran in the absence of diplomatic channels is a recipe for an accidental, perilous clash."

U-turn on North Korea

With only six weeks to go before key midterm US elections, Trump will be seeking to appeal to his hard-right voter base from the dais of the General Assembly.

Trump used his debut address 12 months ago to threaten to "totally destroy" North Korea.

But returning to New York, Trump hailed "tremendous progress" to halt Pyongyang’s nuclear and ballistic missile tests and said that a year later it was a "much different time."

"Chairman Kim has been really very open and terrific, frankly, and I think he wants to see something happen," Trump said after meeting South Korean President Moon Jae-in.

Also making his second address at the General Assembly, French President Emmanuel Macron is expected to take issue with Trump’s America-First policy and make the case for strengthening the rules-based multilateral order.

Macron is championing the Paris climate agreement on reducing greenhouse gas emissions that Trump ditched in June, arguing it would harm the US economy. — AFP