"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."
Iranian media on Thursday appeared unfazed by the US president's threat.
Iranian news agency Tasnim said the announcement was "not a new development, as the United States has been trying for years to block any financial and economic ties with Iran."
Iran had "learned how to circumvent these restrictions and has become very skilled at doing so," Tasnim wrote on Telegram.
Trump said on Tuesday that Washington and Tehran were not currently holding negotiations following the expiry of a 60-day deadline for the two sides to reach a final peace agreement.
"There are no talks or conversations going on, or scheduled, with the Islamic Republic of Iran," Trump wrote on Truth Social.
The statement came a day after Trump told Fox News that US government representatives were in direct contact with Iran's Islamic Revolutionary Guard Corps (IRGC).
Trump has repeatedly made claims about alleged talks or the status of negotiations with Iran that Tehran has subsequently denied.
The 60-day deadline, set out in a preliminary agreement reached in June, expired on Monday without a final peace deal. The two sides remain at odds over several issues, including Iran's nuclear program.
The US has imposed a naval blockade on Iranian shipping and ports, while Tehran has attacked commercial vessels in the Strait of Hormuz, the crucial waterway between Iran and Oman through which about one-fifth of the world's oil passed before the war erupted.
with AP and EFE
