The United States and Iran this week resumed Oman-mediated talks in Geneva aimed at averting the possibility of military action, after Washington dispatched two aircraft carriers, jets and weaponry to the region to back its warnings.

In a Fox News interview with Trump's daughter-in-law Lara, which was taped on Thursday, Witkoff said the president was "curious" about Iran's position after he had warned them of severe consequences in the event they failed to strike a deal.

"I don't want to use the word 'frustrated,' because he understands he has plenty of alternatives, but he's curious as to why they haven't... I don't want to use the word 'capitulated,' but why they haven't capitulated," he said.

"Why, under this pressure, with the amount of seapower and naval power over there, why haven't they come to us and said, 'We profess we don't want a weapon, so here's what we're prepared to do'? And yet it's sort of hard to get them to that place."

The US envoy also confirmed in the interview that he had met with Reza Pahlavi, the exiled son of Iran's last shah and a critic of the current authorities, who has not returned to the country since before the 1979 Islamic Revolution that ousted the monarchy.

"I met him at the direction of the president," Witkoff said, without providing further details.

"I think he's strong for his country, cares about his country. But this is going to be about President Trump's policies."

US-based Pahlavi last week told a crowd in Munich that he was ready to lead the country to a "secular democratic future" after Trump said regime change would be best for the country.

Witkoff's comments come after Iranian Foreign Minister Abbas Araghchi said a draft proposal for an agreement with Washington would be ready in a matter of days.

Trump said on Thursday that Iran had at most 15 days to make a deal on concerns starting with its nuclear programme.

As talks between the two nations continued in Geneva, Iran's supreme leader Ayatollah Ali Khamenei on Tuesday said that Trump would not succeed in destroying the Islamic republic.

Western countries accuse the Islamic Republic of seeking to acquire nuclear weapons, which Tehran denies, though it insists on its right to enrichment for civilian purposes.

Iran, for its part, is seeking to negotiate an end to sanctions that have proven to be a massive drag on its economy, which played a role in sparking anti-government protests in December.