US President Donald Trump has warned Iran of “big problems” if it resumes the nuclear programme it agreed to curb in a 2015 international accord.
Speaking at the White House with French President Emmanuel Macron, Mr Trump called the Iran deal “insane”.
Mr Macron, who is lobbying Mr Trump to preserve the deal, said it was possible to forge a new Iran accord.
The US president has been threatening to reject an extension of the Obama-era nuclear pact by a 12 May deadline.
Germany’s Chancellor Angela Merkel is due to visit the US capital on Friday to make a last-minute bid to dissuade Mr Trump from potentially torpedoing the Iran agreement.
“It won’t be so easy for them to restart,” Mr Trump said in the Oval Office on Tuesday when a journalist asked him about the possibility of Iran relaunching its nuclear programme if the deal is scrapped.
“They’re not going to be restarting anything. They restart it they’re going to have big problems, bigger than they’ve ever had before.”
Iranian Foreign Minister, Javad Zarif, later told the Associated Press Iran would “most likely” abandon the nuclear accord if the US pulled out.
He told the news agency that Washington would only damage its talks with North Korea by proving the US reneges on its promises.
On Monday, Iranian President Hassan Rouhani threatened “severe consequences” if the US withdrew from the deal.
Mr Trump said on Tuesday: “If Iran threatens us in any way, they will pay a price like few countries have ever paid.”
Mr Macron, on a three-day visit to the US, is the first foreign leader to be treated to a state visit during the Trump presidency.
At a joint news conference on Tuesday, he said he had had a very frank discussion with Mr Trump.
The French president also told reporters he believed it was possible to forge a new agreement to address concerns about Tehran.
“We want sustainable stability and I believe the discussions we’ve had together make it possible to open the way, to pave the way for a new agreement,” said Mr Macron.
Under the deal, Tehran agreed to mothball its nuclear programme, which it maintains was for peaceful civilian purposes, in return for an easing of economic sanctions.