The US Treasury has sanctioned 17 vessels and a network of shipping companies that it says carry Iranian oil and petrochemicals to Asian markets.
It described the move as effectively neutralising the vast majority of Iran's remaining shadow fleet.
The action, announced on Thursday by the Office of Foreign Assets Control (OFAC), falls under Operation Economic Outcast. It was taken under Executive Order 13902, which targets Iran's petroleum sector and other key parts of its economy.
"Treasury is starving the tyrannical regime in Tehran of the money it uses to wage war in the region," said Treasury Secretary Scott Bessent. He added that no enabler of Iranian sanctions evasion is safe from the department's authorities.
The designated tankers are flagged across a dozen registries, including Comoros, Panama, the Bahamas, Palau, Cameroon, Vanuatu and Hong Kong.
Treasury said they are owned by firms based in the Marshall Islands, mainland China, Hong Kong, the United Kingdom and the British Virgin Islands.
Many have moved large volumes: the Cameroon-flagged SHENZHEN is cited for over 3.5 million barrels of Iranian crude since November 2025, while the Panama-flagged STARWAY has carried over three million barrels of naphtha.
A dozen firms were designated for operating in Iran's petroleum sector and five for its petrochemical sector.
Treasury also removed two vessels, HAKUNA MATATA and PINOCCHIO, from its sanctions list.
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They were designated in June 2025 but were taken off the shadow fleet and sold to non-sanctioned, US-aligned operators. OFAC said this shows how delisting can follow a demonstrated change in circumstances.
Operation Economic Outcast was announced by Bessent on August 24, this year and dubbed "Economic D-Day".
It aims to cut off the networks, facilitators and financial channels Iran uses to smuggle oil, launder money and fund terror. Treasury says it is working with partners including the European Union, the United Kingdom and Gulf states.
Treasury said the latest step builds on the US military blockade, which it credits with sharply reducing Iranian oil shipments outside the blockade lines.
It said the Iranian regime is "running out of options" as its economy weakens.
All property of the designated parties in the US or in the control of US persons is now blocked.
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The same applies to entities owned 50% or more by them. Foreign financial institutions that knowingly facilitate significant transactions for the designated parties risk secondary sanctions, including loss of US correspondent account access.
Non-US persons face exposure for doing business with Iran, and OFAC's whistleblower incentive programme offers rewards for information leading to enforcement actions above $1 million.
Treasury said it will keep monitoring and disrupting attempts to evade sanctions, and that the ultimate goal of sanctions is behavioural change rather than punishment.
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