Donald Trump announces 'economic warfare' against Iran

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.

"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."