President Donald Trump has declared that if the Iranians "restart their nuclear programme, they will have bigger problems than they have ever had before".
President Trump issued his warning alongside French President Emmanuel Macron in the Oval Office, where the two allies discussed the multinational nuclear agreement, the war in Syria and trade issues during a day of meetings at the White House.
President Trump was asked by reporters if he might be willing to stay in the Iran agreement on nuclear enrichment. He replied, "People know my views on the Iran deal. ... It's insane, it's ridiculous. It should have never been made."
Iranian Foreign Minister Mohammad Javad Zarif warned the Trump administration that pulling out would undermine America's talks with North Korea by proving the US reneges on its promises.
He said in an interview that if President Trump withdraws, Iran would "most likely" abandon the deal as well.
Speaking before President Trump's comments with Mr Macron, Mr Zarif added that Iran would no longer be bound by the deal's international obligations.
That would free Iran to resume enrichment activity beyond the limits imposed by the 2015 accord.
President Trump remains publicly undecided on the deal, saying on Tuesday "no one knows" what he will do at the deadline he set to determine America's position.
But he reminded his French counterpart of what he sees as flaws in the agreement, which he said fails to address ballistic missiles or Iran's activities in Yemen or Syria.
President Trump suggested he was open to "doing something" on the Iran agreement as long as it was done "strongly."
He told Mr Macron, "We could have at least an agreement among ourselves very quickly".
But when he was asked by reporters what that agreement would be, President Trump said, "You'll find out."
During the press conference, Mr Macron added that he and President Trump discussed pursuing a "new agreement" with Iran on the broader regional concerns, including Syria.
But it was not clear whether President Trump would be willing to keep the US in the current deal, known as the Joint Comprehensive Plan of Action, in the meantime.
US military and intelligence officials have urged the president not to pull out of the agreement, arguing it has halted Iran's nuclear programme.