The United States has signaled a sharp escalation in economic pressure on Iran, with U.S. President Donald Trump warning that third countries trading with Tehran could face significant trade penalties. The announcement adds a new dimension to Washington’s response to unrest in Iran, while raising questions about enforcement, legal authority and international reaction.

Trump Announces Tariff Threat on Iran’s Trade Partners

In a post on Truth Social on Monday, U.S. President Trump said that any country conducting business with the Islamic Republic of Iran would be hit with a 25% tariff on all trade with the United States. He said the measure would take effect immediately and described the decision as final, without providing additional clarification.

Under U.S. trade rules, tariffs are paid by American importers bringing goods into the United States from the targeted countries, potentially raising costs across multiple sectors.

Unclear Scope and Legal Basis

Despite the sweeping language of the announcement, there was no official documentation published on the White House website outlining how the policy would be implemented. It remains unclear whether the tariffs would apply to all of Iran’s trading partners or only selected countries, and what legal authority would be used to impose them. The White House did not respond to requests for comment.

Iran has been under extensive U.S. sanctions for years. As a member of OPEC, it exports much of its oil to China, while Türkiye, Iraq, the United Arab Emirates and India are also among its key commercial partners.

International Reactions Begin to Emerge

China reacted critically to the tariff threat, with its embassy in Washington saying Beijing would take “all necessary measures” to protect its interests. A spokesperson said China opposes unilateral sanctions and so-called long-arm jurisdiction, adding that tariff and trade wars do not produce winners.

Japan and South Korea, both of which concluded trade agreements with the United States last year, said they were closely monitoring developments. South Korea’s trade ministry said it would consider appropriate steps once U.S. measures become clearer, while Japan’s deputy chief cabinet secretary said Tokyo would assess potential impacts before responding.

Pressure Builds Amid Iran Protests

The tariff warning comes as Iran faces its most significant anti-government demonstrations in years. The unrest follows last year’s 12-day war between Iran and U.S. ally Israel, as well as U.S. military strikes on Iranian nuclear facilities in June.

President Trump has said the United States may meet Iranian officials and that he has been in contact with Iran’s opposition, while also warning of possible military action. Tehran, for its part, said it is keeping communication channels open with Washington as Trump considers next steps.