US President Trump's letter to Iran's Supreme Leader Ali Khamenei included a two-month deadline for reaching a new nuclear deal, one US official and two sources briefed on the letter told Axios, the latter reports.

But it isn't clear whether the two-month clock begins from the time the letter was delivered, or from when negotiations start. But if Iran rejects Trump's outreach and doesn't negotiate, the chances of US or Israeli military action against Iran's nuclear facilities would dramatically increase.

Two weeks ago in an interview with Fox News, Trump revealed that he sent a letter to the Iranian leader proposing direct negotiations.

A day later Trump said the US is "down to the final moments" with Iran.

"We can't let them have a nuclear weapon. Something is going to happen very soon. I would rather have a peace deal than the other option, but the other option will solve the problem," he said.

The letter was delivered a few days ago by Trump envoy Steve Witkoff to the president of the United Arab Emirates Mohammed Bin Zayed (MBZ) in a meeting in Abu Dhabi.

A day later, MBZ's envoy Anwar Gargash traveled to Tehran and gave the letter to Iranian Foreign Minister Abbas Araghchi.

The sources said Trump's letter to Khamenei was "tough." On the one hand, it proposed negotiations on a new nuclear deal, but on the other hand warned of consequences if Iran rejects the offer and continues to push forward with its nuclear program.

Trump said in the letter that he doesn't want open-ended negotiations and mentioned a two-month period for getting a deal, two sources said.

Before the letter was delivered to the Iranians, the White House briefed several US allies, including Israel, Saudi Arabia and the UAE, about its contents, a US official and a source with knowledge told Axios.