US announces Iran port blockade: The laws governing passage through the Strait of Hormuz

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.

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.

This route is reportedly free of mines, according to a map issued by Iran’s National Security Commission and shared by Lloyd’s List, 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.

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 has been charging fees for maritime traffic diverted from 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.”

Hence, while Iran has not ratified UNCLOS, it shouldn’t undermine its core principles.

Even if the argument were raised that both Iran and the US have signed, and not ratified, the VCLT, the UNCLOS — many of whose core provisions are considered customary international law — are binding to some effect.

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.

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.

Iran’s strategic allies, China and Russia, vetoed Bahrain’s UN Security Council Resolution condemning the blockade. Tehran exports approximately 90 per cent of its crude to China and is in a tie-up with Russia for the production of its Shahed drones.

The US strategy and its legality

By mirroring this strategy, Washington may be able to tip the scales in its favour by pressuring Iran’s allies dependent on crude exports from Hormuz to persuade Tehran to return to the negotiation table and give up the Strait. And, oil exports from the waterway have been the lifeline of Iran’s cash-strapped economy.

Speaking to reporters after placing the blockade, Trump said, “They’d like to make a deal, very badly,” referring to Iran. “Iran will not have a nuclear weapon,” he reiterated, the key sticking point between the two sides.

China on Tuesday called the US blockade “dangerous and irresponsible.” Beijing sourced 13.4 per cent of its oil imports from Iran last year, according to a Reuters report. Russian Foreign Minister Sergey Lavrov arrived in Beijing after the blockade.

Trump said that the US Navy will “interdict every vessel in International Waters that has paid a toll to Iran”. “No one who pays an illegal toll will have safe passage on the high seas,” he added.

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.

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.

Trump’s announcement signals that international organisations have been left toothless due to a lack of consensus to secure collective interests. Now, the US is likely to veto a resolution at the UNSC.

As far as allied support for Washington is concerned, PM Keir Starmer said that the UK will not participate in the US’ blockade. The UK recently held a virtual conference to rally support for collective action against Iran. French President Emmanuel Macron and Starmer will co-chair a conference on Friday aimed at restoring freedom of navigation.

On the other hand, Saudi Arabia cautioned the US that Iran could retaliate by shutting the Bab al-Mandeb, the Red Sea chokepoint where the Houthis (Tehran’s proxy group in Yemen) have previously caused disruptions, The Wall Street Journal reported.

The passage, which accounts for 12% of global oil trade, has become the kingdom’s lifeline for oil exports since the Strait of Hormuz was blocked.