Can Iran prevent ships from passing through the strait of Hormuz?

By Argenis RODRIGUEZ (maritime lawyer)

The Strait of Hormuz is one of the main “chokepoints” in international maritime transport, that is,“narrow waterways where sea routes converge due to geography.”¹ Its importance for the global trade oil cannot be understated. Indeed, according to estimates from the US Energy Information Administration (EIA), in 2025, about 20 million barrels of oil and oil products passed through the Strait of Hormuz per day. “That is nearly $600bn (£447bn) worth of energy trade per year.”²

A complete or partial disruption of navigation through these chokepoints severely disrupts international trade, given the sudden increase in shipping freight and insurance premiums as vessels are forced to take alternative routes to reach their destinations. This directly impacts daily life, since it is ultimately consumers who bear the rise of goods and service prices.
The importance of transit through the Strait of Hormuz is evident in the draft resolution discussed in the United Nations Security Council in early April 2026, which “demanded that Iran immediately cease all attacks on shipping and any attempt to impede transit or freedom of navigation in the strait.”³
Although the resolution was vetoed by Russia and China, it was supported by 11 of the 15 members of the Security Council, which demonstrates the enormous importance to the international community of resuming unimpeded transit through the Strait of Hormuz.

International straits and the right of transit passage

Given the necessity of ensuring the uninterrupted traffic of merchant ships through these chokepoints, the United Nations Convention on the Law of the Sea (hereinafter “UNCLOS”) has taken on the task of directly regulating navigation through straits used in international navigation in its Part III, which covers articles 34 to 45.
In these straits used in international navigation, specifically those governed by Part III of UNCLOS, one of the following regimes applies:

• Transit passage: applies to straits which are used for international navigation between one part of the high seas or an exclusive economic zone and another part of the high seas or an exclusive economic zone, such as the Strait of Hormuz. (Art. 37)
• Innocent passage: applies to straits used for international navigation, which:
  – are formed by an island of a State bordering the strait and its mainland, if there exists seaward of the island a route through the high seas or through an exclusive economic zone of similar convenience with respect to navigational and hydrographical characteristics, such as the Messina Strait (Art. 38(1)); – and between a part of the high seas or an exclusive economic zone and the territorial sea of a foreign State, such as the Gulf of Aqaba (Art. 45(1)(b)).

There are also international straits that are excluded from Part III of UNCLOS entirely, for instance, straits that have a high seas corridor between each border, or straits regulated in whole or in part by long-standing international conventions in force.
The Strait of Hormuz is bordered by Iran and Oman, and most of its aquatic space is entirely within the territorial sea of these countries. Therefore, vessels transiting the Strait of Hormuz enjoy the right of transit passage enshrined in UNCLOS, which grants them greater freedom of navigation than the right of innocent passage that would normally apply when a vessel sails through the territorial sea of another state. Since the Strait of Hormuz is the world’s most important trade chokepoint, it is necessary to ensure that ships passing through it are guaranteed safe and uninterrupted navigation, and this is achieved thanks to the right of transit
passage.

Regarding the justification of the right of transit passage through international straits, it has been said that: “The extension the breadth of the territorial sea to 12 nautical miles resulted in the so called ‘territorialization’ of about 116 international straits, resulting in an important restriction of the freedom of navigation.” The maritime powers realized that a more precise regime for passage of ships through straits was urgently needed⁴ ; the lesser navigational right of non-suspendable innocent passage was simply not sufficient.”⁵

“A regime of transit passage is also crucial to the maintenance of world peace and order. By relieving littoral states of the political burdens associated with the role of gatekeeper, the transit passage rules minimize the danger that strait states will be drawn into international conflicts.”⁶

As can be seen from the preceding lines, the right of transit passage is somewhat closer to the freedom of navigation that prevails on the high seas, than to the right of innocent passage, being necessary to maintain the fluidity of international trade.

Regulation of transit passage

According to article 37 of 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.
Transit passage through international straits allow a grIraneater freedom than innocent passage through territorial sea, since overflight over the strait is allowed in transit passage; on the contrary, innocent passage does not allow overflight of aircrafts.

Pursuant to Article 39 UNCLOS, ships and aircraft making use of the transit passage must observe the following:
a) proceed without delay through or over the strait;
b) refrain from any threat or use of force against the sovereignty, territorial integrity or political independence of States bordering the strait;
c) refrain from any activities other than those incident to their normal modes of continuous and expeditious transit;
d) comply with other relevant provisions of Part III of UNCLOS.

It is noteworthy that from the phrase “other than those incident to their normal modes of continuous and expeditious transit” the doctrine has held that submarines can navigate submerged, since that is their normal mode of navigation.⁷ This is another manifestation of the superior freedom of the right of transit passage compared to the right of innocent passage.

Article 39 also establishes certain specific duties that ships must observe; in this regard, they
shall:
a) comply with generally accepted international regulations, procedures and practices for safety at sea, including COLREG;
b) comply with generally accepted international regulations, procedures and practices for the prevention, reduction and control of pollution from ships.”

Likewise, ships may not carry out any research or survey activities without the prior
authorization of the States bordering straits. (Article 40 UNCLOS).

The coastal states surrounding the international strait have limited powers to ensure the transit
of ships and aircraft. In summary, according to Article 41 of UNCLOS, these powers are as
follows:
a) Designate sea lanes and prescribe traffic separation schemes for navigation, which shall conform to generally accepted international regulations.
b) Substitute other sea lanes or traffic separation schemes for any sea lanes or traffic separation schemes previously designated or prescribed by them, after giving due publicity.
c) Indicate all sea lanes and traffic separation schemes designated or prescribed by them
on charts to which due publicity shall be given.

Legislative powers over transit passage

According to Article 42 UNCLOS, States bordering straits may adopt laws and regulations
relating to transit passage through straits, in respect of all or any of the following:
a) the safety of navigation and the regulation of maritime traffic, as provided in article 41;
b) the prevention, reduction and control of pollution, bIrany giving effect to applicable international regulations regarding the discharge of oil, oily wastes and other noxious substances in the strait; c) with respect to fishing vessels, the prevention of fishing, including the stowage of fishing gear;
d) the loading or unloading of any commodity, currency or person in contravention of the
customs, fiscal, immigration or sanitary laws and regulations of States bordering straits.

Such laws and regulations shall not discriminate in form or in fact among foreign ships or in their application have the practical effect of denying, hampering or impairing the right of transit passage. Examples of measures that have the practical effect of denying, hampering or impairing the right of transit passage include charging a fee for simply crossing the strait, or requiring prior authorization granted by the coastal state to cross it.

Enforcement powers of the coastal States

Pursuant to Article 44 of UNCLOS: “States bordering straits shall not hamper transit passage and shall give appropriate publicity to any danger to navigation or overflight within or over the strait of which they have knowledge. There shall be no suspension of transit passage.”

From the previously cited articles it is clear that Oman and Iran, as a general rule, cannot impede or suspend the passage of ships transiting the Strait of Hormuz.

Now, does this mean they cannot exercise enforcement measures at all? Yes, of course they can, although in very specific cases. Article 233 of UNCLOS makes it clear that the bordering States may take appropriate enforcement measures against foreign ships, except those with sovereign immunity, that have committed a violation of the laws and regulations referred to in article 42, paragraphs 1(a) and (b), which refer to the safety of navigation, the regulation of maritime traffic and the prevention, reduction and control of pollution.

This leaves out the two remaining cases of paragraph 1 of Article 42, referring to fishing vessels and vessels that contravene the customs, tax, immigration or sanitary laws and regulations of the coastal States; therefore, it remains unclear whether the states bordering the strait could exercise jurisdiction against vessels that violate these regulations. However, in the specific case of fishing in the Strait of Hormuz, it could in itself be a violation of the safety regulations imposed by the States, which could therefore take enforcement action measures against the vessel that is fishing.

It is also unclear whether coastal States could take enforcement measures against ships that carry out research or survey activities without prior authorization of such States. If such activity violates safety regulations, it is likely that enforcement measures could be taken.

Iran’s position as a non-party to UNCLOS

The analysis becomes more complex when considering that Iran is not a State Party to UNCLOS, although it is a signatory to the convention. Additionally, it is uncertain whether the right of transit passage established in UNCLOS can be considered customary international law and, therefore, binding on all States. Although the United States considers the right of transit passage to be part of customary international law, there is no real consensus on this matter.⁸

It’s interesting to highlight that Iran submitted a declaration while signing the 1982 Convention, stating that it would only recognize the right of transit passage of ships of states which had ratified the UNCLOS.⁹

The above could be seen by some as meaning that Iran does not have a strict obligation to allow passage through the Strait of Hormuz in cases where its security is threatened, especially to US ships, considering that the United States is also not a party to UNCLOS.

However, the author is of the opinion that, despite the few grey areas that may exist in this case, Iran cannot unilaterally close the Strait of Hormuz. Firstly, Iran is not the only state bordering the strait; Oman also borders it and, in fact, most of the shipping lanes in the strait lie in Omani territorial waters¹⁰ so, in a way, closing the passage to the Strait of Hormuz would violate Oman’s sovereignty by preventing ships from transiting through its territorial waters.

Secondly, even if we were to admit that Iran is not obligated to respect the right of transit passage, it would still be prevented from closing the Strait of Hormuz, since the 1958 Convention on the Territorial Sea and the The Contiguous Zone, of which Iran is a State Party, establishes in its Article 16, paragraph 4, a non-suspendable innocent passage in the following terms: “There shall be no suspension of the innocent passage of foreign ships through straits which are used for international navigation between one part of the high seas and another part
of the high seas or the territorial sea of a foreign State.” Therefore, preventing passage through the Strait of Hormuz, or imposing a toll to allow the passage, would clearly violate the non- suspendable innocent passage that Iran is fully obliged to recognize pursuant to the 1958 Convention.

Finally, it is worth asking whether the current armed conflict between Iran and the United States gives Iran the right to impede passage through the Strait of Hormuz, since UNCLOS is primarily designed to govern the oceans in times of peace. In principle, the right of transit passage through the Strait of Hormuz cannot be impeded or suspended, even if one of the states bordering the strait is a party to an armed conflict.¹¹ Therefore, Iran cannot suspend the passage of ships of neutral states through the Strait of Hormuz; however, it could be argued that Iran may impede the passage of US warships perceived as a threat to its security; as von Heinegg states: “a belligerent is not obliged to leave unmolested enemy vessels and aircraft transiting a strait overlapped by its territorial sea. Neutral shipping and neutral aircraft, however, continue to enjoy the right of transit passage.”¹²

1. Weitz. Strategic Maritime Chokepoints: Global Shipping and Maritime Industry Perspectives, p. 1. Available:​ https://usnwc.edu/_images/portals/0/News-and-Events/EMC-Workshops/Sea-Control-and-Foreign-Policy/Weitz-Strategic-Maritime-Chokeopoints.pdf ↩︎
2. Gavin Butler, Toby Mann, Patrick Jackson and BBC Persian. Why the Strait of Hormuz matters so much in the Iranian war. Accessed on April 9, 2026. Available: https://www.bbc.com/news/articles/c78n6p09pzno ↩︎
3. Security Council: Russia and China veto resolution on Strait of Hormuz. Accessed on April 17, 2026. Available: https://news.un.org/en/story/2026/04/1167261 ↩︎
4. Franckx, E., Razavi, A. The Strait of Hormuz, published in The Proceedings of the Symposium on the Straits used for International Navigation, p. 56. Available: https://tudav.org/wp-content/uploads/2018/04/navigation_straits.pdf ↩︎
5. William L. Schachte, Jr. and J. Peter A. Bernhardt. International Straits and Navigational Freedoms, Virginia Journal of International Law Vol. 33:527, pp. 530, 531. Available: https://files.pca-cpa.orgpcadocs/2017-06/3.%20Ukraine%20-%20Revised%20Memorial%20-%20Legal%20Authorities/3 %20Ukraine%20-%20Revised%20Memorial%20-%20Legal%20Authorities/UAL-128.pdf ↩︎
6. Ibid, p. 531 ↩︎
7. Yoshifumi Tanaka. The International Law of the Sea, p. 103. Available: https://files.pca-cpa.org/pcadocs/2017-06/3.%20Ukraine%20-%20Revised%20Memorial%20-%20Legal%20Aut h orities/3.%20Ukraine%20-%20Revised%20Memorial%20-%20Legal%20Authorities/UAL-141.pdf ↩︎
8. Bashir Ali Abbas. Assessing the ‘Law of the Sea’ A Case for the US’ Right of Passage in the Strait of Hormuz.
   Institute of Peace and Conflict Studies, p. 7. Available: https://www.ipcs.org/issue_briefs/issue_brief_pdf/ipcs%20sr205_international%20law%20and%20strait%20of%20hormuz_baabbas_january2020.pdf ↩︎
9. Ibid. ↩︎
10. Ibid, p. 7. ↩︎
11. Wolff Heintschel von Heinegg. The Law of Naval Warfare and International Straits, published in International Law Studies – Volume 71, The Law of Armed Conflict: Into the next millennium, p. 279. Available: https://digital-commons.usnwc.edu/cgi/viewcontent.cgi?article=1627&context=ils ↩︎
12. Ibid. ↩︎