Introduction

On April 12, 2026, President Trump announced via Truth Social that the United States Navy would begin “BLOCKADING any and all Ships trying to enter, or leave, the Strait of Hormuz.”  The social media announcement was followed within hours by a formal CENTCOM press release confirming that the blockade would take effect on April 13 at 10 a.m. ET “in accordance with the President’s proclamation.” Exactly one week later, the blockade produced its first vessel seizure: on April 19, the U.S. Navy intercepted, disabled, and boarded the Iranian-flagged container ship M/V TOUSKA in the north Arabian Sea as it attempted to enter the Persian Gulf in violation of the blockade. The TOUSKA remains in U.S. custody. The seizure brings to the fore aspects of the law of naval warfare that have remained largely dormant since the Second World War and brings into effect a legal regime distinct from the maritime law enforcement regime that generally prevails under the law of the sea.

The Law of Naval Blockades

Naval blockades are a recognized instrument of belligerent warfare under customary international law, codified most authoritatively in the 1994 San Remo Manual on International Law Applicable to Armed Conflicts at Sea. Under Articles 93–108 of the Manual, a legally valid blockade must satisfy several requirements: it must be formally declared and notified to all belligerents and neutral states; it must be effective, meaning it genuinely prevents ingress and egress from the enemy’s coast; it must be applied impartially to vessels of all nations; and it must not bar access to neutral ports or coasts, nor cut off the supply of essential humanitarian goods to the civilian population. The blockaded area must be clearly defined, and sufficient warning must be given to neutral shipping so that vessels may alter course. Although novel, the declaration by presidential social media post alone could satisfy the Manual’s declaration requirement.  If it was insufficient alone, the subsequent official CENTCOM press release and Notice to Mariners broadcast likely provides the requisite formality. Under the Manual, any vessel that breaches, or attempts to breach, a lawfully declared blockade becomes subject to capture, along with its cargo.

M/V TOUSKA

This legal framework was invoked in practice on April 19, 2026. According to the CENTCOM press release, guided-missile destroyer USS SPRUANCE (DDG 111) intercepted M/V TOUSKA as it transited the north Arabian Sea toward the Straits of Hormuz bound for Bandar Abbas, Iran. U.S. forces issued multiple warnings, informing the Iranian-flagged vessel it was in violation of the U.S. blockade. After TOUSKA’s crew failed to comply with repeated warnings over a six-hour period, USS SPRUANCE directed the vessel to evacuate its engine room, then disabled the ship’s propulsion by firing several rounds from the destroyer’s 5-inch MK 45 Gun into the engine room. U.S. Marines from the 31st Marine Expeditionary Unit subsequently boarded the non-compliant vessel, which remains in U.S. custody.  Since the blockade was declared, U.S. forces had directed 25 commercial vessels to turn around or return to Iranian ports. This action was thus the first actual capture under the blockade.

Legal Authorities: Blockade, OFAC Sanctions, and the Law of Prize

Three distinct legal frameworks converge on the TOUSKA boarding. First, and most significantly, the capture was executed under the law of armed conflict rather than domestic law enforcement authority. San Remo Manual Articles 118–124 establish the general right of belligerent warships to visit and search merchant vessels outside neutral waters — but that regime applies to neutral vessels only where there are reasonable grounds for suspicion of contraband or blockade-running. That is not the operative framework here. The TOUSKA is an Iranian-flagged vessel, and therefore an enemy merchant ship subject to San Remo Article 135. It states directly: “Enemy vessels, whether merchant or otherwise, and goods on board such vessels may be captured outside neutral waters. Prior exercise of visit and search is not required.” The vessel falls within none of Article 136’s enumerated exemptions — it is not a hospital ship, a cartel vessel, a humanitarian transport, nor any other protected category.

At this point, the Law of Prize applies.  Under San Remo, Article 138 governs the procedure: “Capture of a merchant vessel is exercised by taking such vessel as prize for adjudication.” Diversion from the vessel’s declared destination is an available alternative. The Law of Prize is implemented by statute at 10 U.S.C. Chapter 883 (§§ 8851–8880), titled simply “Prize,” which details the U.S. legal requirements for capture, custody, and adjudication of enemy vessels and their cargo by U.S. naval forces.

CENTCOM’s announcement on the TOUSKA, however, did not describe the action as capture and it remains to be seen whether TOUSKA will be subject to legal proceedings as a prize.  An alternative legal regime is available under U.S. sanctions law: TOUSKA has been sanctioned by the U.S. Office of Foreign Assets Control (OFAC) since 2020 for its links to Islamic Republic of Iran Shipping Lines. Its owner, Mosakhar Darya Shipping Co., is also subject to U.S. Treasury sanctions. As a result, two legal avenues are available under U.S. law. TOUSKA could be adjudicated as prize and become property of the U.S. government.  Alternatively, the vessel could be adjudicated under forfeiture statutes similar to those relied on for the December seizure of MT SKIPPER.  Only time will tell.

Conclusion

The TOUSKA seizure marks a historically significant legal departure from the earlier pattern of U.S. maritime interdictions. Prior actions like the MT Skipper and the MT Marinera (a/k/a Bella 1) arose in the context of the Coast Guard-led Venezuela sanctions campaign under a maritime law enforcement framework applying US federal criminal law. The TOUSKA, by contrast, was by all indications captured as an enemy merchant vessel under San Remo Manual Article 135.  The U.S. blockade of Iranian ports has activated the long-dormant law of prize requiring merchant shipowners and marine insurers to become familiar with a legal regime they may have thought was consigned to the dustbin of history.  For more information contact us at info@chaloslaw.com.