US President Donald Trump has said he is holding off a military attack on Iran planned for Tuesday at the request of Gulf states as "serious negotiations are now taking place".

In a post on Truth Social, he said he had been asked to do so by the leaders of Qatar, Saudi Arabia and the United Arab Emirates.

He said he had been informed a deal would be made that is "very acceptable" to the US, adding there would be "NO NUCLEAR WEAPONS FOR IRAN!"

But he warned the US would be ready to "go forward with a full, large scale assault of Iran, on a moment's notice" if there was no acceptable deal.

A senior Iranian military commander told the US not to make "strategic mistakes and miscalculations again".

Trump's latest announcement on Iran comes amid a drop in his approval rating and as polls show the war is increasingly unpopular at home.

Some 64% of voters believe it was the wrong decision to go to war with Iran, according to a New York Times/Siena poll published on Monday.

The survey also found that just 37% of voters approve of Trump's job performance as president. The polling underscores the challenge Republicans face in the midterm elections, in a moment of growing public frustration with the war and Trump's handling of the economy and immigration, among other issues.

Israeli and US forces began massive air strikes on Iran on 28 February, while Tehran retaliated by firing drones and missiles at Israel and US targets in countries across the Gulf.

A major factor at play here is the fear Gulf Arab states have over how Iran is likely to retaliate after any further attacks by the US.

Iran is known to retain a significant number of drones and missiles with which it could resume its full-scale attacks on neighbouring states, their airports, petrochemical facilities and even the crucial desalination plants that provide drinking water as summer temperatures in the Gulf build up.

Talking to reporters later, Trump called it "a very positive development, but we'll see whether or not it amounts to anything".

He said: "We've had periods of time where we had, we thought, pretty much getting close to making a deal, and it didn't work out. But this is a little bit different."

Trump said there seemed to be "a very good chance" of an agreement with Iran, adding: "If we can do that without bombing the hell out of them, I would be very happy."

A ceasefire agreed in April meant to facilitate talks has largely been observed despite occasional exchanges of fire.

Iran has also continued to control the Strait of Hormuz, effectively closing the vital waterway through which around 20% of the world's oil and liquefied natural gas travels.

The move, which Iran has said is in retaliation for US and Israeli attacks, has sent oil prices soaring globally.

The US, for its part, has been enforcing a blockade of Iranian ports to exert pressure on Tehran to agree to its terms.

Late on Monday, Iran's Tasnim news agency published what it said were comments by Supreme Leader Mojtaba Khamenei, warning that new fronts would be opened where the enemy had little experience and would be highly vulnerable.

Tasnim appeared to have reposted Khamenei's quotes from 12 March. Some Iranian news outlets have taken to republishing his previous written messages.

Earlier on Monday, Iran said it had responded to the latest US proposal and that exchanges with Washington were continuing through Pakistani mediators.

Iranian media earlier reported the US had failed to make any concrete concessions to Tehran.

On Sunday, Trump had warned that "for Iran, Clock is Ticking, and they better get moving, FAST, or there won't be anything left of them".

Several days ago, the US president had said the truce was on "massive life support" after rejecting Tehran's demands, labelling them "totally unacceptable".

Esmail Baghaei, an Iranian foreign ministry spokesperson, insisted they were "responsible" and "generous".

According to Iran's semi-official Tasnim news agency, Iran's demands included an immediate end to the war on all fronts - a reference to the continued Israeli attacks against Iran-supported Hezbollah in Lebanon - a halt to the US naval blockade of Iranian ports, and guarantees of no further attacks on Iran.

They also reportedly included a demand for compensation for war damage and an emphasis on Iranian sovereignty over the Strait of Hormuz.

Iran's semi-official Fars news agency said on Sunday that Washington had set five conditions in response to Tehran's proposal.

They reportedly included a demand that Iran keep only one nuclear site in operation and transfer its stockpile of highly enriched uranium to the US.

Trump suggested on Friday he would accept a 20-year suspension by Iran of its nuclear programme - a major sticking point between the two countries - in what appeared to be confirmation of a shift in position away from a demand for a total end to it.

The US and its European allies claim Iran is seeking to develop nuclear weapons by enriching uranium. Tehran has repeatedly said its nuclear programme is solely for peaceful purposes.