‘Effective immediately’: Trump threatens 25% tariff on countries doing business with Iran

US President Donald Trump on Monday announced a sweeping trade warning against countries engaging with Iran, saying Washington would impose new penalties on such nations.

"Effective immediately, any Country doing business with the Islamic Republic of Iran will pay a Tariff of 25% on any and all business being done with the United States of America. This Order is final and conclusive. Thank you for your attention to this matter!," Trump wrote on Truth Social.

China, Brazil, Turkey and Russia are among economies that have business relations with Iran, according to a report by The Associated Press.

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Trump said on Sunday that the US may meet Iranian officials and that he was in contact with Iran’s opposition, while intensifying pressure on Tehran’s leadership, including threats of military action over the killing of protesters.

Although airstrikes were among the options under consideration, White House press secretary Karoline Leavitt said diplomacy remained the administration’s priority.

"While airstrikes were one of many alternatives open to Trump, 'diplomacy is always the first option for the president'," she told reporters on Monday.

Leavitt added that Washington was receiving mixed signals from Tehran.

"What you're hearing publicly from the Iranian regime is quite different from the messages the administration is receiving privately, and I think the president has an interest in exploring those messages," she said.

Iran’s leaders, whose regional influence has weakened, are confronting widespread protests that began over severe economic hardship and have since escalated into open calls for the overthrow of the clerical establishment.

Iranian Foreign Minister Abbas Araqchi said Tehran was reviewing proposals from Washington but described them as inconsistent with US threats.

"Communications between (US special envoy Steve) Witkoff and me continued before and after the protests and are still ongoing," he told Al Jazeera.