An Iranian woman walk past anti-US mural depicting Iran and US negotiation table, painted on the outer walls of the former US embassy, in Tehran. AFP
The order, effective from Saturday, called for a fresh "imposition of tariffs" on countries still doing business with Iran.
It comes amid heightened tensions between Washington and Tehran, with an American naval group led by an aircraft carrier in Middle Eastern waters and indirect talks held on Tehran's nuclear program in Oman on Friday.
The levies "may be imposed on goods imported into the United States that are products of any country that directly or indirectly purchases, imports, or otherwise acquires any goods or services from Iran", the order said.
Trump issued a threat of 25 percent tariffs on any country trading with Iran last month.
This order establishes a process for his administration to impose tariffs on goods from those countries.
The rate is to be determined by Secretary of State Marco Rubio, although the order specifies that it could be "for example" 25 percent, the level first mentioned by the US president in mid-January.
Tariffs would affect trade with a number of countries including Russia, Germany, Turkey and the United Arab Emirates.
More than a quarter of Iran's trade is with China, with $18 billion in imports and $14.5 billion in exports in 2024, according to World Trade Organization data.
The talks on Friday in Muscat, mediated by Oman, were the first between the two foes since the United States joined Israel's war with Iran in June with strikes on nuclear sites.
"We likewise had very good talks on Iran," Trump told reporters on board Air Force One en route to his Mar-a-Lago resort in Florida, adding, "we're going to meet again early next week."
Diplomatic relations between Iran and the United States broke down after the 1979 Islamic Revolution brought the current government to power, and direct engagement has been rare in the decades since.
*This story was edited by Ahram Online.
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