President Trump said he had sent a letter to the Iranian government seeking to negotiate a deal to prevent Tehran from acquiring a nuclear weapon.

He said the letter was sent Wednesday and addressed to Ayatollah Ali Khamenei, Iran’s supreme leader. The White House did not immediately respond to a request to provide the letter or further describe its contents.

“There are two ways Iran can be handled: militarily, or you make a deal,” Mr. Trump told Maria Bartiromo in an interview aired Friday on Fox Business. “I would prefer to make a deal, because I’m not looking to hurt Iran. They’re great people.”

The move is a sharp pivot for Mr. Trump, who in 2018 withdrew the United States from a nuclear deal with Iran, unraveling the signature foreign policy achievement of his predecessor, Barack Obama.

Iran did not immediately provide a response.

In the interview, Mr. Trump described the letter as saying, “I hope you’re going to negotiate because it’s going to be a lot better for Iran.”

“If we have to go in militarily, it’s going to be a terrible thing for them,” he said, adding: “The other alternative is we have to do something because you can’t let them have a nuclear weapon.

On Thursday, Mr. Trump talked more broadly about his desire to see the world’s countries eliminate their nuclear weapons. He said he hoped to negotiate denuclearization efforts with China and Russia as well.

“It would great if everybody would get rid of their nuclear weapons,” he told reporters in the Oval Office.