Washington DC - President Donald Trump on Friday signed an executive order threatening tariffs on Iran's trade partners, after he pledged a further round of talks with Tehran next week.

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.

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Trump issued a threat of 25% 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%, 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 since the US 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."

After the talks, the US announced new sanctions to curb Iran's oil exports, including targeting 14 vessels.