• Toby Irwin

Maritime Law in the Strait of Hormuz

On Friday, the British oil tanker ‘Stena Impero’ was seized by Iranian special forces in the Strait of Hormuz and was escorted to the port of Bandar Abbas. The 23 crew members remain detained in Iran, though are reportedly in “good health” (1). A second British ship, ‘MV Mesdar’, was also stopped by Iran though was later allowed to continue on its journey (2).


(Source: BBC News)


According to officials in Tehran, the seizure of Stena Impero was due to supposed violation of international maritime law. As the Islamic Revolution Guards Corps stated, “"UK tanker ship, Stena Impero, has been detained by the vessels unit of the IRGC Navy's First Naval Zone at the request of the Ports and Maritime Organization's office of Hormuzgan province for disregarding international maritime rules and regulations as it was passing through the Strait of Hormuz this afternoon" (3).


One can doubt this claim though. Consider for a moment the United Nations Convention on the Law of the Sea. According to it, of which Iran is a signatory, the territorial sea of a state extends 12 nautical miles from the baseline of a state’s internal waters. Within this territory states possess absolute sovereignty and jurisdiction (4). However, unlike internal waters, foreign vessels have the right to transit territorial seas for a number of reasons.



Innocent passage, as set out in Section 3 of the UN Convention, establishes that a vessel may traverse a coastal state’s territorial waters provided it is not “prejudicial to the peace, good order or security of the coastal state”. Twelve criteria are established for what might be considered passage that is not innocent, among which is the threat or use of force, the exercise of weapons, the spread of propaganda and the carrying out of surveying (5). One can seriously doubt whether Stena Impero was violating any of these, and thus one is tempted to note that the seizure of the tanker was not due to maritime law violations. Rather, it can be seen as a political gesture in retaliation against the British seizure of an Iranian vessel near Gibraltar just a few weeks prior (6). Indeed, as the UK operator of the tanker confirmed, the ship was “in full compliance with all navigation and international regulations” (6).



Moreover, there now arises the news that the British tanker was not even within Iranian territorial waters, instead being within Oman’s. The defence secretary Penny Mordaunt confirmed this yesterday, subsequently describing it as a “hostile act” (8). Looking at the above map one can see how easy it is for contending parties to disagree on the legality of the situation; was the ship in Omani or Iranian territorial waters? That said, having gone over the rights of passage for ships such as the Stena Impero it is plainly clear that the ship was not within the baseline – or internal waters – of Iran. The result is that regardless of which territorial waters the ship was in, it was not an illegal transit. The question now is what the implications will be for ships hoping to enjoy freedom of navigation. Further, how will the involved parties respond in order to maintain international maritime law in the region?


For more information regarding the rights of ships and the concept of freedom of navigation, see here: https://sites.tufts.edu/lawofthesea/chapter-three/.



(1) https://www.bbc.co.uk/news/uk-49059066

(2) http://en.farsnews.com/newstext.aspx?nn=13980429000027

(3) http://en.farsnews.com/newstext.aspx?nn=13980429000027

(4) https://sites.tufts.edu/lawofthesea/chapter-two/

(5)https://www.un.org/depts/los/convention_agreements/texts/unclos/unclos_e.pdf

(6) https://www.theguardian.com/world/2019/jul/04/royal-marines-gibraltar-tanker-oil-syria-eu-sanctions

(7) https://uk.reuters.com/article/uk-mideast-iran-tanker-britain-statement/uk-operator-of-seized-stena-impero-says-vessel-in-compliance-with-regulations-idUKKCN1UE2QA?feedType=RSS&feedName=domesticNews

(8) https://www.independent.co.uk/news/world/middle-east/iran-tensions-oil-tanker-seizure-oman-stena-impero-gulf-defence-secretary-a9013496.html


At the time of writing, Toby Irwin is a third year student at the University of St Andrews. He is studying International Relations. Areas that interest him the most are UK defence strategy and foreign policy.

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