US President Donald Trump has announced unprecedented “economic warfare” against Iran amid stalled negotiations with Tehran, warning countries supporting Iran of economic consequences.

“No one has given the Islamic Republic of Iran a greater opportunity to make a Deal than me,” Trump wrote on his Truth Social platform, adding that Tehran had “failed to take it”.

“Therefore, today, I am announcing the MOST CRUSHING ECONOMIC OPERATION EVER TAKEN AGAINST ANY COUNTRY!” Trump wrote.

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“This will be Economic Warfare and Isolation on an unprecedented scale,” he added.

Any country that allows its financial institutions, businesses, airports or government entities to provide “any type of lifeline to Iran” would itself face “TREMENDOUS Economic Consequences,” Trump wrote.

It was not immediately clear what that meant for major economies with close ties to Iran, including China.

But Trump said his prohibitions would include things like oil smuggling, cash transfers and co-operation through exchange houses and ship registries and front companies.

“It all needs to stop NOW. You know who you are,” Trump said, imploring US allies “to stand with the United States of America to isolate, and defeat, the Iran threat”.

Trump threatens to bomb allied country

The economic warfare threat comes days after Trump threatened to attack to attack Oman if it interfered with US efforts to take control of the Strait of Hormuz as the America’s war with Iran drags on.

Oman, a US ally, borders the United Arab Emirates, Yemen and Saudi Arabia, and sits near the strait.

“If Oman gets in the way, we’ll bomb the s*** out of them,” the US president said in a phone interview with Fox News chief foreign correspondent Trey Yingst on Monday local time.

Speaking with reporters in the Oval Office later the same day, Trump again criticised Omanian officials over their ongoing talks with Iran regarding shipping through the strait.

“I don’t think they behaved very well, but we’d handle them very easily, just like we do other things,” he said.

“If Oman gets in the way, we’ll bomb the s*** out of them,” the US president said in the phone interview.

Speaking with reporters in the Oval Office later the same day, Trump again criticised Omanian officials over their ongoing talks with Iran regarding shipping through the strait.

“I don’t think they behaved very well, but we’d handle them very easily, just like we do other things,” he said.

Monday marked the end of a 60-day memorandum of understanding between the US and Iran, which the two countries agreed to in June to negotiate an end to the war and reach an agreement on Iran’s nuclear program.

- With AP