Following a deadlock in ceasefire talks, the US has announced a complete blockade of Iranian ports in response to Iran’s effective closure of the Strait of Hormuz.
While Washington’s move may appear to mirror Iran’s strategy at first glance, it is essentially aimed at putting pressure on the energy-consuming countries, which Iran considers “friendly” and whose ships it has allowed to pass through the strait.
Both the US and Iranian strategies have led to claims and counter-claims over their legality, involving terminology such as “territorial waters” and “international waters”. Here’s a look at the international legal framework that governs maritime passage and maritime combat in the context of the strategies being deployed by both countries.
The Iran strategy
The Strait of Hormuz is Iran’s main leverage at the negotiation table. Since the US-Israeli alliance began the war on February 28, Iran has maintained a chokehold on the strait by targeting vessels and laying mines. The move triggered one of the world’s worst energy shocks as the narrow passage accounted for around 20% of the global energy trade.
According to Tehran’s 10-point proposal, it has sought to legitimise its control over the strait by demanding US recognition of its sovereignty over the passage.
In March, a parliamentary commission in Iran approved plans to impose tolls on vessels transiting the strait. According to reports, Tehran also suggested splitting the toll collected with Oman and said in a social media post that Hormuz does not fall under international waters, but the territorial waters of Iran and the Gulf nation.
While the laws of naval warfare bring some degree of legality to mine-laying and blockades, Tehran has reportedly leveraged its position by charging a fee of $2 million for each vessel transiting the chokepoint by diverting maritime traffic around Iran’s Larak Island.
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This route is reportedly free of mines, according to a map issued by the Islamic Revolutionary Guard Corps (IRGC), and it lies within Iran’s territorial waters. Diplomatic circles have dubbed this set-up the “Ayatoll booth.”
According to a Financial Times report, Iran is also said to be considering a $1 per barrel fee in cryptocurrency. Tehran has reportedly sought to use the revenue as reparations for the war.
Is this legal?
The Iranian strategy violates a comprehensive set of international maritime delimitation laws and puts Iran in a grey zone even with regard to laws of naval warfare.
Unlike the Suez Canal, navigation along the Strait of Hormuz is governed by the United Nations Convention on the Law of the Sea (UNCLOS), which stipulates free, unhindered navigation for all vessels transiting the route.
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While the Strait of Hormuz may lie in the territorial waters of the two countries, both westbound and eastbound shipping lanes — under the International Maritime Organization’s (IMO) Traffic Separation Scheme (TSS) — lie entirely within the territorial waters of Oman.
This means that Tehran is insisting on charging fees in Omani-administered waters.
Notably, the maritime borders were established in a treaty between Iran and Oman in July 1974, and the countries joined the IMO in June 1958 and July 1974, respectively.
According to the 1969 Vienna Convention on the Law of Treaties (VCLT), which is “regarded as the mother of all treaties,” a country that has signed but not ratified a treaty “is obliged to refrain from acts which would defeat the object and purpose of a treaty.”
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Hence, while Iran has not ratified UNCLOS, it shouldn’t undermine its core principles.
While both Iran and the US have signed, and not ratified, the Vienna Convention (both Iran and the US) the rule is still considered binding on them.
The US strategy and its legality
Washington’s NATO partners, including the UK, France and Germany, have openly distanced themselves from the war in West Asia. Italy and Spain refused US access to a key airbase and blocked its airspace for military use, respectively.
Against this backdrop, Iran allowed ships of US allies — France, Japan and South Korea — to pass through the Strait of Hormuz alongside Indian, Chinese, Russian, Pakistani and Iraqi vessels.
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This strategy opens a window for Iran to avoid a collective global backlash and aims to widen a split between the US and its traditional allies.
Now, with its own blockade, Washington may be able to pull the tide in its favour.
US President Donald Trump said that the US Navy will “interdict every vessel in International Waters that has paid a toll to Iran”.
The US Central Command said the blockade will be enforced “impartially against vessels of all nations entering or departing Iranian ports and coastal areas”. This includes all Iranian ports in the Persian Gulf and the Gulf of Oman.
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While Trump has insisted that the aforementioned methods will eventually pave the way for “safe passage on the high seas,” the move of blocking Iran-linked vessels may be a violation of freedom of navigation as much as Iran’s strategy.
Notably, the US has not ratified UNCLOS either, which means that at some point, the world might end up in a scenario where both parties are flouting a framework neither has formally committed to.
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