US 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.