US President Donald Trump has published an expletive-laden post on social media in which he threatened to destroy Iran's power plants and bridges if it failed to meet his Tuesday deadline to reopen the Strait of Hormuz to all shipping.
He repeated an earlier threat to unleash "hell" but told US media there was a "good chance" of a deal being reached with Tehran.
Iran mocked his ultimatum, dismissing it as "helpless, nervous and stupid".
Trump's new threat came after he announced that the second crew member of a US fighter jet downed over Iran had been successfully rescued in an operation deep inside hostile territory.
Both the US and Iran had scrambled to locate the US serviceman in a mountainous region of south-western Iran. The pilot of the F-15 had been recovered shortly after the aircraft was shot down on Friday.
The incident came after more than a month of war, as Iran continued to respond to US and Israeli air strikes with attacks on Gulf nations allied to the two countries.
Iran has also significantly impeded transit in the Strait of Hormuz, a vital shipping lane through which about a fifth of the world's oil and gas normally passes, leading to skyrocketing global oil prices and fears of higher inflation around the world.
The disruption led Trump in March to announce a series of deadlines for Iran to reopen the strait. On Sunday he took to his Truth Social platform to reaffirm this demand.
He said: "Tuesday will be Power Plant Day, and Bridge Day, all wrapped up in one, in Iran. There will be nothing like it!!! Open the [expletive] Strait, you crazy [expletive]', or you'll be living in Hell - JUST WATCH! Praise be to Allah. President DONALD J. TRUMP"
Afterwards, he told Fox News there was a "good chance" a deal would be reached on Monday, but he was considering "blowing everything up and taking over the oil" if a deal to end the war was not reached quickly.
Later, the US president posted again - "Tuesday, 8:00 P.M. Eastern Time!" - an apparent extension of the deadline originally meant to expire on Monday, 6 April.
Trump has postponed deadlines for the reopening of the Strait of Hormuz several times.
On 21 March, Trump initially threatened to "obliterate" Iran's power plants if the Strait of Hormuz was not "FULLY OPEN" within 48 hours.
Two days later, he said he would not launch strikes for another five days - until 28 March - while "good" and "productive" talks with Iran continued. Iran denied any contact between its officials and the Trump administration had taken place.