The recent regional conflicts which led to exchanges of aerial attacks between Israel and Iran has reemphasised the importance of the Strait of Hormuz, a vital maritime chokepoint through which one third of the world's liquefied natural gas and one quarter of total global oil production passes. As a strategically vital waterway from both a regional and global perspective, navigation rights in the Straits are based on long-standing customary international law and an evolving legal regime.
Constituting a 90 nautical miles-long sea passage, the Strait is only 21 nautical miles wide at its narrowest point. ‘Third country’ shipping has the extensive right, as determined by the 1982 UN Convention on the Law of the Sea (UNCLOS), to transit the Straits. However, as the Islamic Republic of Iran has signed but not ratified UNCLOS, Tehran reserves its position on the right of ‘innocent passage’ through the Straits, a right considered inferior to globally recognised ‘transit rights’.[1]
While the Strait of Hormuz is recognized as an international waterway, sovereignty over its waters is divided between Iran and the Sultanate of Oman. As the volume of shipped hydrocarbons has increased, ships transiting the Straits mainly travel through Oman’s territorial waters as these provide the easiest navigable routes.
From an international legal perspective, any action to protect shipping in the Straits and ensure the safe passage of vessels requires a UN Security Council mandate. This Insight assesses the prospects for enhancing regional security tensions through international agreements to clarify the maritime laws in the Strait of Hormuz.
Transit Passage and Innocent Passage
In accordance with the 1982 UN Convention on the Law of the Sea (UNCLOS), third country shipping retains extensive rights to transit the Straits of Hormuz along with other narrow waterways between coastal states.
In addition to provisions of ‘innocent passage’ set out in the 1958 Geneva Convention on the Territorial Sea and Contiguous Zone, UNCLOS, which subsumed the four treaties that constituted the 1958 Geneva Convention on the High Seas, also established the principle of ‘transit passage’ between one part of the high seas or between the exclusive economic zones of one state and another.[2]
‘Transit passage’ rights as set out Article 38 of UNCLOS relate to ‘the exercise in accordance with this part 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’.[3] While littoral states have the right to regulate transit passage in respect to navigational safety, shipping traffic, pollution, fishing, and border and customs management[4], UNCLOS is explicit that for vessels observing their legitimate rights, ‘bordering straits shall not hamper transit passage’.[5]
In terms of ‘innocent passage’, Article 17 of UNCLOS subsumed the provisions of the 1958 Geneva Convention by stipulating that ‘ships of all States, whether coastal or land-locked, enjoy the right of innocent passage through the territorial sea’.[6]
At the same time, ‘innocent passage’ assumes that it is ‘not prejudicial to the peace, good order or security of the coastal State’; to this end, ships must desist from the threat or use of force or any of a range of activities that might threaten the security of a littoral state.[7] Similarly, the innocent passage of warships through the territorial sea of a littoral state is subject to the ‘laws and regulations’ of that state and must abide by the same provisions regarding the threat or use of force.[8]
In relation to the nature of passage rights for shipping through the Straits of Hormuz, it is worth also taking into account the International Court of Justice (ICJ) opinion in 1969 in the North Sea Continental Shelf Cases, which were concerned with the delimitation of the undersea continental shelf of the North Sea between Denmark, the Netherlands and the Federal Republic of Germany.
Based on applicable international law, the Court held that the boundary lines in question should be resolved according to equitable principles based on natural prolongation of each country’s land territory under the sea, rather than in accordance with the principle of equidistance outlined in the 1958 Geneva Convention. As the Federal Republic of Germany had not ratified the 1958 Convention, the equidistance principle was therefore not a rule of customary international law.[9]
The ICJ’s North Sea Continental Shelf suggested that the existing conventions on the international law of the sea do not supersede a state’s territorial rights in its claimed maritime zones. In the context of the Straits of Hormuz, this suggests that while Iran and Oman should permit civil and military shipping to pass through the Straits in accordance with UNCLOS, the two states are also permitted to enforce their laws and regulations in their territorial waters under their control. Transiting ships should thus observe their duties in accordance with their obligations as set out in UNCLOS.[10]
In the case of both UNCLOS and the earlier 1958 Convention, Iran signed but did not ratify the agreements. In signing UNCLOS, Iran indicated that it would only apply the new ‘transit passage’ regime to those states that ratified the Convention; in other cases, the 1958 Convention would apply.[11]
Iran has also reserved its position on the right of ‘innocent passage’ through the Straits; the implication of this is that ‘innocent passage’ rights could be regarded as weaker than ‘transit rights’, given that a state can deny passage if it is deemed not to be innocent. Nevertheless, both UNCLOS and the 1958 Convention prohibit the unjustified prevention of ‘innocent passage’, and no notification or authorization needs to be secured by any transiting vessel regardless of their activity.
The existing regime as codified in the Law of the Sea therefore consolidates passage rights through narrow straits, with third country shipping having the extensive right to invoke such transit rights as set out in international legal precedent.
The Stena Impero incident, 2019
However, as Iran has not ratified UNCLOS, Tehran reserves its position on the right of ‘innocent passage’ through the Straits, a right considered inferior to transit rights.
Iran’s sovereign rights as a coastal state also mean that the country can establish and enforce laws for territorial waters, though it cannot prevent passage through international straits, including for military vessels. Nevertheless, Iran’s rights in its waters mean that duties of passage have to be observed by transiting ships.
The international legal regime is less ambiguous in the case of shipping impeded or detained in the Straits of Hormuz and adjacent seas.
On 19 July 2019, Iranian vessels stopped and impounded the Stena Impero, a British-flagged vessel owned by a Swedish shipping company. Although allegations were made that the ship was actually detained in Oman’s territorial waters, the Iranian justification claimed that the Stena Impero had endangered other vessels by disregarding local navigational rules and colliding with an Iranian fishing boat.
Nevertheless, the United Kingdom government suspected that the incident was a retaliatory measure against the detention, two weeks earlier, by the Royal navy of the previously Panamanian-flagged tanker Grace 1 near Gibraltar due to suspicions that the vessel was carrying oil to Syria in violation of international sanctions.
Whether or not the detention took place in Omani waters, the Iranian justification for the detention of Stena Impero was questionable. The action undoubtedly entailed multiple violations of UNCLOS. Article 39 of the Convention[12] obliges ships exercising the right of transit to proceed without delay through narrow waterways: Stena Impero was clearly not contravened this provision. There was also no evidence that Stena Impero was in violation of recognized sea lanes and maritime traffic rules.
As was noted previously, Iran has never ratified the 1958 Convention on the High Seas or UNCLOS, but has in practice generally not interfered with the passage of shipping through the Straits of Hormuz. If the case of the Stena Impero had been brought before an international court of tribunal, the UK may have been able to argue that UNCLOS now represents customary international law.
At the same time, a claim that the stopping of the Stena Impero was a legally justified countermeasure against the detention of Grace 1 would be unlikely to be accepted by the ICJ or other international courts.[13] Article 49 of the Draft Articles on Responsibility of States for Internationally Wrongful Acts states that countermeasures may only be taken against illegal acts and that any violation must directly affect the state that claims the right to take such measures.[14] As the Grace 1 was previously registered in Panama and did not carry an Iranian flag, Iran’s rights were therefore not in question.
Security Implications
In terms of existing international legal conventions, there is evident ambiguity over the rights of ships passing through the Straits of Hormuz. While the right of ‘innocent passage’ could arguably be viewed as customary law, the position is less clear in relation to ‘transit passage’. While littoral states such as Iran are not permitted to impede shipping according to international norms, these states still exercise territorial rights in their sea areas that are supported by some international legal precedents.
The applicability of UNCLOS to the Straits of Hormuz is intricately related to a range of political questions, territorial disputes and security fears.[15] While such disputes are ongoing, they are likely to deter states from joining UNCLOS. The unwillingness of some local states, including Iran and Oman, to ratify the Convention further undermines the force of the Convention. At the same time, the fact that the US is not an UNCLOS signatory influences the position of many other states. It is therefore incumbent on great powers to ensure the convention operates more effectively, perhaps through a regional accord that clarifies the legal regime in the Straits.
In the view of many nations, including the United States, customary law as codified in UNCLOS and the 1958 Convention confirms the right of passage in the case of Straits of Hormuz. In practice, while Iran has periodically threatened to close the waterway in response to regional security developments, both commercial and military shipping has continued to pass through the Straits without interference.
Conclusion
In the context of ‘innocent passage’ and ‘transit rights’ in the Straits of Hormuz, it is remains problematic to claim that these rights constitute customary international law as assumed by UNCLOS and international legal opinion. In addition to Iran and Oman, other states, including non-parties such as Turkey and Venezuela, and full parties such as Russia and Spain, have reserved their positions on passage rights through straits that they claim to exercise full or partial territorial control over.
Such reservations are particularly pertinent to those states that have refrained from ratifying the UN Convention on the Law of the Sea. This would also apply to the United States, which has availed itself of the right for its civil and military shipping to transit the Straits of Hormuz, even though it has not signed or ratified UNCLOS.
From an international legal perspective, it is difficult to justify intervention by external powers to protect shipping in territorial waters without a UN Security Council mandate. Ongoing political questions and territorial disputes will prevent states from joining UNCLOS, especially given that the US is not an UNCLOS signatory. Despite this, the immense strategic importance of the Straits of Hormuz should give sufficient incentive to great powers to ensure the convention operates more effectively.
Disclaimer:
The views and opinions expressed in the INSIGHTS publication series are those of the individual contributors and do not necessarily reflect the official policy or position of Rabdan Security & Defense Institute, its affiliated organizations, or any government entity. The content published is intended for informational purposes and reflects the personal perspectives of the authors on various security and defence-related topics.
References
Cataldi, Giuseppe, ‘The Strait of Hormuz’, Questions of International Law, Vol. 76 (2020), pp. 5-19 (https://www.qil-qdi.org/the-strait-of-hormuz/).
Guilfoyle, Douglas, 'Iran and the Strait of Hormuz: some initial thoughts', EJIL: Talk! Blog of the European Journal of International Law, 2 February 2012 (https://www.ejiltalk.org/iran-and-the-strait-of-hormuz-some-initial-thoughts/) [accessed 1 September 2021].
Hartwig, Matthias, ‘Tanker Games – The Law Behind the Action’, EJIL: Talk! Blog of the European Journal of International Law, 20 August 2019 (https://www.ejiltalk.org/tanker-games-the-law-behind-the-action/).
Kraska, James, ‘Legal Vortex in the Strait of Hormuz’, Virginia Journal of International Law, Vol. 54, No. 2 (2014): 323-366.
Lotta, Alexander and Kawagishi, Shin, ‘The Legal Regime of the Strait of Hormuz and Attacks Against Oil Tankers: Law of the Sea and Law on the Use of Force Perspectives’, Ocean Development & International Law, Vol. 53, Nos. 2–3 (2022), pp. 123–146.
Nadimi, Farzin, ‘Clarifying Freedom of Navigation in the Gulf’, PolicyWatch 3154, The Washington Institute for Near East Policy, 24 July 2019 (https://www.washingtoninstitute.org/policy-analysis/clarifying-freedom-navigation-gulf).
Serdy, Andrew, ‘Iran: what the law of the sea says about detaining foreign ships in transit’, The Conversation, 23 July 2019 (https://theconversation.com/iran-what-the-law-of-the-sea-says-about-detaining-foreign-ships-in-transit-120816).
Ulfstein, Geir, ‘How International Law Restricts the Use of Military Force in Hormuz’, EJIL: Talk! Blog of the European Journal of International Law, 27 August 2019 (https://www.ejiltalk.org/how-international-law-restricts-the-use-of-military-force-in-hormuz/#:~:text=Ships%20shall%20not%20threaten%20or,to%20protect%20their%20own%20ships).
United Nations, Convention on the Territorial Sea and the Contiguous Zone, Geneva, April 1958 (https://www.gc.noaa.gov/documents/8_1_1958_territorial_sea.pdf).
United Nations Convention on the Law of the Sea (henceforth UNCLOS), Articles 17-19, 30, 38-44, 10 December 1982 (https://www.un.org/Depts/los/convention_agreements/texts/unclos/part3.htm).
[1] Matthias Hartwig, 'Tanker Games – The Law Behind the Action', EJIL: Talk! Blog of the European Journal of International Law, 20 August 2019 (https://www.ejiltalk.org/tanker-games-the-law-behind-the-action/).
[2] United Nations, Convention on the Territorial Sea and the Contiguous Zone, Section III, Articles 14-23, Geneva, April 1958 (https://www.gc.noaa.gov/documents/8_1_1958_territorial_sea.pdf).
[3] United Nations Convention on the Law of the Sea (henceforth UNCLOS), Part III, Article 38, 10 December 1982 (https://www.un.org/Depts/los/convention_agreements/texts/unclos/part3.htm).
[4] UNCLOS, Part III, Article 42(1).
[5] UNCLOS, Part III, Article 44.
[6]UNCLOS, Part II, Article 17, (https://www.un.org/Depts/los/convention_agreements/texts/unclos/part2.htm).
[7] UNCLOS, Part II, Article 19.
[8] UNCLOS, Part II, Article 30.
[9] International Court of Justice, ‘North Sea Continental Shelf Cases’, Judgment of 20 February 1969, ICJ Reports 1969 (https://www.icj-cij.org/public/files/case-related/52/052-19690220-JUD-01-00-EN.pdf).
[10] Giuseppe Cataldi, ‘The Strait of Hormuz’, Questions of International Law, Vol. 76 (2020), pp. 5-19 (http://www.qil-qdi.org/wp-content/uploads/2020/12/02_Asian-Straits_CATALDI_FIN.pdf).
[11] Douglas Guilfoyle, 'Iran and the Strait of Hormuz: some initial thoughts', EJIL: Talk! Blog of the European Journal of International Law, 2 February 2012 (https://www.ejiltalk.org/iran-and-the-strait-of-hormuz-some-initial-thoughts/).
[12] UNCLOS, Part III, Article 39.
[13] Andrew Serdy, 'Iran: what the law of the sea says about detaining foreign ships in transit', The Conversation, 23 July 2019 (https://theconversation.com/iran-what-the-law-of-the-sea-says-about-detaining-foreign-ships-in-transit-120816).
[14] United Nations General Assembly, UNGA Resolution 56/83, Annex, International Law Commission, ‘Draft Articles on Responsibility of States for Internationally Wrongful Acts’, Article 49, 12 December 2001 (https://legal.un.org/ilc/texts/instruments/english/draft_articles/9_6_2001.pdf).
[15] Farzin Nadimi, 'Clarifying Freedom of Navigation in the Gulf', PolicyWatch 3154, The Washington Institute for Near East Policy, 24 July 2019 (https://www.washingtoninstitute.org/policy-analysis/clarifying-freedom-navigation-gulf).
