Tanker Games – The Law Behind the Action

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The conflict between some western States and Iran has reached a new phase. Last month, both sides arrested tankers off their coasts. Whereas the political intentions of either side are evident, difficult questions come up with regard to the legal assessment of these actions. They concern the extraterritorial application of a sanction regime, the law of the sea and countermeasures. The post will describe the facts related to the detention of a tanker off Gibraltar (1). It will be investigated if the regime of the transit passage (2) or of innocent passage (3) is applicable under the UN Convention on the Law of the Sea (UNCLOS). Thereafter, the post will study which State may rely on the respective rights (4). The post then will turn to the facts of the second case which happened in the strait of Hormuz (5). It will shortly mention Iran’s right to take measures for the safety of navigation beyond its territorial waters (6), and the regime of countermeasures (7). In part (8) the compatibility of military patrols by western States in the strait of Hormuz with the law of the sea will be studied.

The Facts related to the case off the coast of Gibraltar

On July 4, 2019 the British navy detained the tanker Grace 1, allegedly in the territorial waters of Gibraltar. The vessel was passing through the strait of Gibraltar after having circumnavigated Africa. The chief minister of Gibraltar declared in a press release that the vessel was seized in order to enforce EU sanctions against Syria. The decision was based on the EU regulation 36/2012, a law of Gibraltar of 29 March 2019 and a regulation of Gibraltar of 3 July 2019. According to art. 14 para. 2 of the EU regulation it is prohibited to make available economic resources to corporations listed in Annex 2 to the regulation which includes the Banyas Oil Refinery Company. The chief minister of Gibraltar alleged that the oil carried by the tanker came from Iran and was destined to the refinery; this is denied by Iran.

The EU regulation and the above-mentioned legislation of Gibraltar is applicable on the territory of Gibraltar and the territorial waters. Gibraltar claims territorial waters up to 3 nm.

Grace 1 is owned by a shipping company located in Singapore and flew the flag of Panamá. However, according to the Autoridad Marítima de Panamá the vessel was removed from the open registry of Panamá on 29 May 2019.

Transit Passage

It is generally recognized that this strait falls under art. 37 UNCLOS meaning that all ships enjoy transit passage according to art. 38 UNCLOS. Ships in transit passage must refrain from the threat or the use of force against the coastal States and shall not violate the principles of international law embodied in the Charter of the UN; however a transit passage must not be suspended even if a vessel does not comply with her obligations; ships in transit passage cannot be inspected or detained. Coastal States may regulate the transit passage with regard to the safety of navigation, pollution, fishery and loading and unloading in contravention of their customs, fiscal, immigration or sanitary laws. No other national rules may be imposed on a vessel. However, art. 36 UNCLOS excludes the right to transit passage if a ship enters the territorial waters of a coastal State, if the vessel could have passed through the High Seas or Exclusive Economic Zone. If one accepts that Gibraltar has territorial waters – which is disputed by Spain – the limitation of this zone to 3nm entails that there is a sea beyond the 3nm – it may qualify as exclusive economic zone or as high seas – where vessels would enjoy freedom of navigation. Accepting this the vessel could have lost her right to transit passage by entering the territorial waters of Gibraltar.

Innocent Passage

In this case she would only enjoy innocent passage as provided for by art. 17 of the UNCLOS. If a passage is not innocent it can be denied by the coastal State. A passage is not innocent if it is prejudicial to the peace and security of the coastal State, art. 19 para. 1 of the UNCLOS; the passage shall take place in accordance with the UNCLOS and with other rules of international law. According to art. 19 para. 2 of the UNCLOS a threat or use of force against the sovereignty or a violation of principles of international law under the UN Charter make a transit prejudicial to the peace and security of the coastal State. With regard to illegal arms trade with third States it has been held that this could be a violation of the principles of the UN Charter. As far as UN sanctions against arms trade, which have been issued to this end, there is no doubt that the coastal State can deny a passage which is in conflict with the sanction regime. However, the definition of activities which are prejudicial to the peace and security are defined by art. 19 para. 2 of the UNCLOS. A specific reference to the costal State’s legislation can be found in art. 19 para. 2 lit. (g). A vessel in innocent passage must respect the coastal State’s legislation in the area of safety of navigation, prevention of pollution, of fishery and – when loading and unloading –  the customs, fiscal, immigration or sanitary laws. Additionally, criminal and civil law may be enforced under certain circumstances. There is no indication that other violations of national law of the coastal State can be qualified as prejudicial to peace, thereby excluding the right to innocent passage. It is the very sense of innocent passage that a ship –although sailing in territorial waters – shall as far as possible enjoy an unfettered navigation. It derives therefrom that the imposition of national/EU sanctions – i.e. not UN sanctions – against third States on a ship conducting an innocent passage violates basic principles of the law of the sea.

Holder of the Right to Unencumbered Navigation under the UNCLOS?

Art. 17 UNCLOS reads: “Subject to this Convention, ships of all States, whether coastal or land-locked, enjoy the right of innocent passage through the territorial sea.” In a negative sense one may conclude from this provision that neither the shipping company running the vessel nor the owner of the cargo transported by the ship may rely on the right to innocent passage. In the given case neither the Singapore company which allegedly owns the ship nor Iran who is said to be the owner of the oil transported by the tanker can claim the right to innocent passage. “Ships of all States” implies that only ships having the nationality of a State may refer to the right to innocent passage. The actual holder of the right to innocent passage is the State whose flag the ship is flying and it would be the flag State who would be entitled to defend the rights of innocent passage, for example before the International Tribunal on the Law of the Aea. In the end it is not the ship but the State who enjoys the innocent passage. This corresponds to the provisions on freedom of navigation – art. 87 of the UNCLOS – which qualifies this right as a right of the States.

The legal position of a flagless vessel is not regulated by the UNCLOS. Art. 110 of the UNCLOS conveys the power to warships to visit flagless ships, but it does not rule on the consequences of sailing without a flag. When art. 17 of the UNCLOS establishes the right of ships of all States to innocent passage one may conclude with good reasons that a ship without a flag does not enjoy this right. Access to territorial waters may be blocked. Although the detention of a flagless vessel in territorial waters is not provided for by the UNCLOS, no State may – in case of an arrest of such a ship – avail itself of the right to innocent passage, as it follows from the argumentation above. If sailors are detained, the State of nationality may offer diplomatic protection. With regard to property which has been confiscated, the owner State may bring a claim, however, just referring to the property, not to the law of the sea. Here, the question will arise to what extent sanctions by a State/ the EU may be applied to third States. The EU and its member States persistently objected to the extension of US sanction to EU corporations holding that such sanctions must not have extraterritorial effects. By now, the EU did not implement its sanctions regime against Syria vis-à-vis third States. However, if a ship and its cargo is detained in the territorial waters it is hard to argue that a sanction regime is extraterritorially applied.

From the observations made above one should come to the conclusion that the UK did not violate Iran’s rights under international law when it detained the tanker Grace 1.

Facts related to the detention of the tanker in the strait of Hormuz

On July 2019, Iran arrested the vessel Stena Impero, presumably in the territorial waters of Oman. The vessel is run by a Swedish shipping company and flying the British flag. Iran produced varying justifications, one claiming that the tanker violated navigation rules, another alleging that the ship collided with an Iranian fishing vessel and a third qualifying the detention as a countermeasure.

Iran’s Measures of the Safety of Navigation beyond its Territorial Waters

One may question if Iran was entitled to take measures against the British vessel in the territorial waters of Oman. Such activities certainly constitute a violation of the sovereignty of Oman, but the violation of Oman’s sovereignty does not ipso facto constitute an infringement of the UK’s rights. However, Iran would not be authorized to detain a British ship on the high seas under the given circumstances as here the freedom of navigation prevails over the sovereign interests of a coastal State. Iran is also excluded from detaining the vessel in the territorial waters of Oman, as the UK enjoyed the right to an unfettered navigation in the form of an innocent passage. This right is framed as a protection against the coastal State, however, as part of the broader frame of unencumbered navigation it is a right against all other States. It would be inconsistent to prohibit a State from enforcing measures against a foreign vessel on the high seas while allowing so in the territorial waters of another State. One may come to a different conclusion if one assumes that Oman empowered Iran to take these measures and if these measures are considered legal. However, even Iran did not claim that it got such an authorization. Therefore, Iran’s arguments fall short of a convincing justification.


As the action of Iran constitutes a violation of international law, it could only be justified as a countermeasure, as Iran did. However, this argument must be rejected. According to art. 49 of the Draft on State responsibility an injured State may take countermeasures only against illegal acts. Apart from the violation of obligations erga omnes the violation must affect the State which avails itself of the right to countermeasures. As demonstrated above, Iran’s rights were not violated by the detention of Grace 1 as this ship did not fly the Iranian flag.

Legality of Patrol Mission in the Strait of Hormuz

The last question to be tackled concerns the legality of the establishment of a military mission of control in the strait of Hormuz. The regime in this strait is disputed as Iran did not ratify UNCLOS which introduced the concept of the transit passage in international straits. Iran claims territorial waters within 12nm. This claim is sometimes disputed as it is held that a State cannot claim an outer border of 12 nm without ratifying UNCLOS,thereby accepting the free transit regime in international straits. However, the described connection of the 12 nm zone and the transit passage is not generally recognized. If one excepts the extension of the territorial waters in the strait of Hormuz as a unilateral act, the right to innocent passage would apply as established by the Geneva Convention on Territorial Waters of 1958, ratified by Iran and the USA. But independently from the application of the innocent passage regime or the free passage regime which the USA bases on customary international law the passage rights are limited to an expeditious transit. This, of course, does not encompass any exercise of policing powers in the strait. The control and surveillance in this area is an exclusive competence of the coastal States. An international military mission in the strait to control navigation without the consent of Iran is a violation of the law of the sea. It could be justified only as a countermeasure for the infringement of the right to unfettered navigation by Iran. But one should be aware that such an infringement of Iran’s sovereign rights in its territorial waters – even if justified under international law as a countermeasure – will be a further step towards a potential war.


The detention of ships in transit passage or innocent passage in order to enforce a national sanction regime against a third State by the coastal State is illegal under international law. The right to unimpeded navigation under the law of the sea is not conveyed to flagless vessels. A State other than the flag State cannot avail itself of this right. In case of the loss of property a State may seek protection. However, the seizing of property in the territorial waters for a violation of a sanction regime established by the coastal State is not an illegal extraterritorial application of national law. A coastal State cannot take measures against a vessel for alleged illegal acts beyond its territorial waters. Countermeasures can be taken only by a State injured by internationally illegal acts. A military mission in a strait by non-coastal States is not in conformity with the passage regime in these areas; it could be justified only as a countermeasure.

A different question which has not been investigated here is if a consistent pattern to strangle the economy of another State as the USA does with regard to Iran, e.g. by convincing Panamá to remove all Iranian ships from its open registry thereby making them flagless and by imposing ever stronger economic sanctions even with extraterritorial effects – could not justify a reaction by the affected State in the same way as economic interests of the western States shall justify a mission to keep the strait of Hormuz open.


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Valentin Schatz says

August 21, 2019

Dear Matthias,

thank you for this interesting post!

I have two questions/comments, if you don't mind:

1. According to the UN Website (https://treaties.un.org/Pages/ViewDetails.aspx?src=IND&mtdsg_no=XXI-1&chapter=21&clang=_en) Iran has signed, but not ratified, the 1958 Convention on the Territorial Sea and the Contiguous Zone. Yet you wrote that Iran is a party to the CTSCZ. Could you please clarify?

2. You seem to be taking the view that the EU sanctions regime for Syria (specifically the sanctions applicable to the Baniyas refinery) were applicable based purely on the location of the Grace 1 in Gibraltar's territorial sea because that renders the issue territorial rather than extraterritorial. Yet, if you look into the relevant sanctions regime, assuming that the oil had not yet been Syrian property, was it not an extraterritorial transaction between non-EU nationals (Iran -> Syria) lacking any connection to the EU? Is the sanctions regime applicable to such transactions?

Thank you for you consideration!


Matthias Hartwig says

August 21, 2019

Dear Valentin,

thank you for your most valuable comments. As for your observation related to the ratification of the Geneva Convention on the Territorial Sea of 1958 by Iran you find different statements in the literature. The source you mentioned is certainly most authoritative, therefore one should assume that Iran did not ratify the Convention. However, it does not change the argument, as the innocent passage in territorial waters as laid down in the Convention of 1958 forms part of customary international law.

Regarding your second question I think that it is not relevant where and between whom a contract has been concluded, if the oil in question is in the territory - including the territorial waters - of a State which established a sanction regime prohibiting the export of such oil to a corporation targeted by the sanction regime.

Meanwhile the tanker was released allegedly after Iran promised not to deliver the oil to Syria. There are reports that the ship now is flying the flag of Iran which would mean that it is enjoying the right of innocent passage in territorial waters.

Thank you again for your valuable comments.


Martin Ratcovich says

August 21, 2019

Dear Matthias,

Thank you for your interesting post! According to the press release by HM Government of Gibraltar dated 8 July 2019, the Grace 1 was seized “when it freely navigated into British Gibraltar Territorial Waters ... on a pre-arranged call for provisions and spare parts.” This seems to suggest that the seizure took place when the ship was under neither innocent passage nor transit passage. Rather, it would have taken place when the Grace 1 was merely “hovering” or otherwise simply being present within territorial waters thus being subject to the full territorial sovereignty of the coastal state (n.b. the limitation to “necessary” measures under art 25 UNCLOS only applies to non-innocent “passage”, which is explicitly defined in art 18 UNCLOS). Although I understand that the merit of my reasoning to large extent depends on facts, I am curious to know what you think about it. Many thanks in advance!

Kind regards,


Matthias Hartwig says

August 22, 2019

Dear Martin,

thank you for your comment. You are right, not all facts are known. My legal conclusions are based on some factual assumptions for which I do not have sufficient evidence. As you mentioned according to the press release of the Government of Gibraltar Grace 1 asked for spare parts and supply. Art. 18 of the UNCLOS includes stopping and anchoring into the notion of innocent passage, "in so far as the same are incidental to ordinary navigation". The taking over of spare parts - which might be necessary for a safe navigation - must be qualified as "incidental to navigation".

Thanks again for your interest.


Abdollah Abedini says

August 25, 2019

Dear Matthias

Thanks for your interesting post. Let me ask a question on the procedure of seizing the prohibited items concerning the sanction regime on Syria. Under Article 26 (2) of Council Decision 2013/255/CFSP of 31 May 2013 concerning restrictive measures against Syria:
“Member States, in accordance with their national legis¬lation and consistent with international law, shall, upon discovery, seize and dispose of items whose supply, sale, transfer or export is prohibited under Article 1 or 2.” (emphasis added)

Based upon the above provision, it seems the Government of Gibraltar should seize and dispose of prohibited items which might be used for internal repression or for the manufacture and maintenance of products, which could be used for internal repression, to Syria. The result of this provision is that the Government of Gibraltar should have only seized and disposed of crude oil of the Grace 1 and not the tanker itself.
On the other hand, one may claim crude oil of the Grace 1 could not be considered as ‘equipment, goods and technology’ mentioned in para. 1 of the Council Decision 2013. So, if it is categorised, as the Government of Gibraltar has claimed, as economic resource which shall be frozen under Article 14 of Council Regulation of 18 January 2012 or Article 28 of Council Decision 2013, the result would be the same as Article 26 (2) of Council Decision 2013 applies through seizing and disposing of items prohibited.
And if one assumes the crude oil of Grace 1 is essentially as an economic resource in the meaning of “assets of every kind, whether tangible or intangible, movable or immovable, which are not funds but can be used to obtain funds, goods or services” (Article1(f) of the Regulation 2012), the same procedure would apply for freezing the crude oil of Grace 1, that is, seizing and disposing of crude oil as an economic resource and consequently, releasing the tanker.
The last point that seems more important is that Syria itself is an exporting oil county. (Syria produced about400,000 barrels per day (bbl/d) of crude and other petroleum liquids in 2010: see here, here and here)
How could it be justified to export crude oil to a county which itself exports its oil to other countries? In this way, could it be presumable the crude oil of Grace 1 as an economic resource regarding Syria an exporting oil county?