"If they don't make a deal, there will be bombing," NBC News said the president told one of its correspondents in an interview late Saturday. It said he also threatened to punish Iran with what he called "secondary tariffs."

Trump's language represented a sharpening of his comment a few days earlier that if Tehran refused to negotiate a new nuclear agreement, "bad, bad things are going to happen to Iran."

It was not clear whether Trump was threatening bombing by US planes alone or in an operation coordinated with Israel.

Israeli Foreign Minister Gideon Saar told Politico late last month that "in order to stop a nuclear Iranian program before it will be weaponized, a reliable military option should be on the table."

Analysts have said Iran may be just weeks away from producing a deliverable nuclear weapon -- though Tehran denies it is building such arms. Either way, such an attack carries a risk of spreading to a wider conflict.

Trump in 2018 pulled the United States out of an agreement to relieve sanctions on Iran in return for curbs on its nuclear program.

Now, in his second term, he has said he is open to talks on a new deal that could reduce the risk of military escalation.

Trump revealed in early March that he had sent a letter proposing such talks to Iran's supreme leader, Ayatollah Ali Khamenei.

Meantime, he has pushed ahead with his "maximum pressure" program of additional sanctions and the threat of military action.

Tehran, deeply suspicious of the US administration after Trump's withdrawal from the original nuclear deal, has refused to negotiate directly with Washington.

On Thursday, Iran's Foreign Minister Abbas Araghchi told the official IRNA news agency that he had delivered a letter responding to Trump's outreach to Oman, which has served as an intermediary in the past.