Iran’s “Closure” of the Strait of Hormuz as a Reprisal to US-Israeli Joint Attack: A Legality Analysis

On the night of February 28, 2026, Reuters, citing European and Iranian sources, reported that Iran’s Revolutionary Guards declared that “no ship is allowed to pass the Strait of Hormuz”, following the US-Israeli joint attack on Iran earlier that day. This “threat” was confirmed on March 2 as an Iranian Revolutionary Guards senior official announced that “the Strait of Hormuz is closed and Iran will fire on any ship trying to pass”. BBC and Reuters also reported on March 2 that global oil prices have jumped after several fuel tankers were attacked near the Strait of Hormuz. As of the afternoon of March 3, crude oil prices have been kept surging for two days. This is by no means the first time in the past year that Iran has resorted to the “closure” of the Strait of Hormuz as a reprisal to foreign military operations. In June 2025, following the US bombing of its three nuclear facilities, Iran threatened to close the Strait of Hormuz, though the timely ceasefire prevented Iran from adopting such measures.

The Strait of Hormuz is the sole maritime passage connecting the Persian Gulf with the Indian Ocean. Data indicates that approximately 20% of global oil consumption transits through this strait. Consequently, the Strait of Hormuz is often termed the “world’s most important oil transit chokepoint.” Precisely because of its strategic significance, the strait has repeatedly served as a “trump card” for Iran in its confrontations with Western nations, particularly the United States and Israel.

This commentary examines the legal status of the Strait of Hormuz during peacetime and periods of armed conflict, based on the relevant provisions of the 1982 United Nations Convention on the Law of the Sea (UNCLOS) and the law of naval warfare. It thereby proceeds to assess the legality of Iran’s proposed “closure” of the Strait.

Legal Status of the Strait of Hormuz in Peacetime: Applicability of the Transit Passage Regime, Unilateral “Closure” not Permitted

It is generally recognized that the navigation regime applicable to an international strait varies depending on its geographical and historical circumstances. The Strait of Hormuz has a narrowest width of approximately 21 nautical miles. Since Oman declared a 12-nautical-mile territorial sea in 1972, the Strait has been overlapped by the territorial seas of its two coastal States, Oman and Iran. It is thus a typical strait to which the “transit passage” regime under the UNCLOS applies. According to Article 38 of the UNCLOS, “transit passage” means “the exercise… of the freedom of navigation and overflight solely for the purpose of continuous and expeditious transit of the strait between one part of the high seas or an exclusive economic zone and another part of the high seas or an exclusive economic zone.” Furthermore, “all ships and aircraft enjoy the right of transit passage” through such straits, and “transit passage shall not be impeded.” This means that vessels and aircraft, including warships and military aircraft, enjoy the right of transit passage through such international straits. Article 44 of the UNCLOS further emphasizes the obligations of coastal States bordering straits used for international navigation, stating that they “shall not hamper transit passage” and that “transit passage shall not be suspended.”

Although Iran has not yet ratified the UNCLOS, and there is some academic debate as to whether the right of transit passage established by the UNCLOS has become customary international law, Iran did sign the UNCLOS on December 10, 1982, the day it was adopted. Pursuant to Article 18 of the 1969 Vienna Convention on the Law of Treaties, Iran is obligated to “refrain from acts which would defeat the object and purpose” of the UNCLOS. Moreover, given that the Strait of Hormuz is not entirely within Iran’s territorial sea, Iran lacks the right to unilaterally “close” the Strait without the express consent of the other coastal State, Oman.

Legal Status of the Strait of Hormuz During Armed Conflicts: The Transit Passage Regime Shall Continue to Apply

An international armed conflict between Iran, the US and Israel has been ongoing since February 28. Given the existence of armed conflicts, can Iran unilaterally “close” the Strait of Hormuz?

The UNCLOS does not explicitly stipulate whether peacetime passage regimes automatically terminate upon the outbreak of an armed conflict, or whether parties to an armed conflict have the right to suspend various passage regimes. However, the Preamble of the UNCLOS states that “matters not regulated by this Convention continue to be governed by the rules and principles of general international law.” Furthermore, Article 311(2) of the UNCLOS indicates that “this Convention shall not alter the rights and obligations of States Parties which arise from other agreements compatible with this Convention and which do not affect the enjoyment by other States Parties of their rights or the performance of their obligations under this Convention.” A combined reading of these provisions suggests an inference that, in principle, passage regimes through international straits should continue to apply during armed conflicts, unless otherwise provided by relevant international treaties or rules of customary international law.

At present, there exists no general international convention specifically regulating passage through straits during armed conflicts. Therefore, solving this issue requires examining the rules of customary law of naval warfare pertaining to passage through international straits during armed conflicts.

The San Remo Manual on International Law Applicable to Armed Conflicts at Sea (the “San Remo Manual”), widely regarded as reflecting contemporary customary law of naval warfare, explicitly affirms the continued “openness” of international straits during armed conflict. Paragraph 27 of the Manual stipulates: “The right of transit passage, which applies in international straits in time of peace, continues to apply in time of armed conflict.” Paragraph 28, addressing warships, specifies that belligerent and neutral warships have the right of transit passage through international straits generally. Furthermore, Paragraphs 32 and 33 stipulate that neutral warships retain the right of innocent passage through international straits of belligerent States. Crucially, where the innocent passage regime through certain straits cannot be suspended under Article 38(1) or Article 45 of UNCLOS, this right remains effective during armed conflicts. Given that warships and military aircraft are subject to more restrictions on passage rights compared to merchant vessels and civil aircraft, the specific provisions of the San Remo Manual outlined above demonstrate that the right of transit passage for warships and military aircraft through international straits must be guaranteed even during armed conflicts. It follows logically that merchant vessels and civil aircraft should likewise retain the right of transit passage.

Additionally, the Newport Manual on the Law of Naval Warfare (2023, 2025), representing the latest collective work primarily by Western scholars of the law of armed conflict, largely reflects the prevailing views of Western States on the contemporary law of naval warfare. Regarding the passage regime through international straits during armed conflict, the Newport Manual also affirms: “The navigational regime applicable to international straits in peacetime continues to apply in situations of international and non-international armed conflict.”

In short, Iran, as a party to the ongoing international armed conflict, lacks the right to “close” the Strait of Hormuz.

Can Iran “Close” the Strait of Hormuz on Grounds of Military Necessity, or Countermeasures?

As early as 2012, a Turkish scholar published a commentary in the American Society of International Law Insights in which he contemplated a scenario where the United States might strike Iranian nuclear facilities and Iran would respond by “closing” the Strait of Hormuz. He concluded that even if Iran were subjected to an attack not authorized by the UN Security Council, Iran would still lack the legal right to “close” the Strait of Hormuz. This conclusion stems from the immense importance of the Strait of Hormuz to international shipping, particularly its critical role in global oil transportation. A “closure” of the Strait would severely disrupt shipping in the Gulf region and cause significant harm to the global economy. This is exactly the case right now.

Moreover, Article 51 of the Draft Articles on Responsibility of States for Internationally Wrongful Acts, adopted by the UN International Law Commission in 2001, emphasizes that “Countermeasures must be commensurate with the injury suffered, taking into account the gravity of the internationally wrongful act and the rights in question.”

Finally, given that the “closure” of the Strait of Hormuz cannot effectively counter US-Israeli joint missile strikes, any Iranian decision to “close” the Strait of Hormuz could not be justified under military necessity. Consequently, the military advantage Iran might gain from such a closure would be “disproportionate” compared to the damage inflicted on international shipping and oil transport.

Conclusion

Considering the relevant provisions of UNCLOS and applicable rules of customary international law governing naval warfare, the transit passage regime should, as a general rule, remain in force in the Strait of Hormuz during armed conflict. Therefore, Iran has not the right under international law to unilaterally “close” the Strait of Hormuz.

Dr. Yinan Bao is an associate research fellow at Huayang Center for Maritime Cooperation and Ocean Governance, and non-resident fellow at ICAS. The thoughts and opinions expressed are those of the author and not necessarily those of the Huayang Center for Maritime Cooperation and Ocean Governance or ICAS.