Trump’s Hormuz Threat: Can the US Take Over the Strait?

US President Donald Trump says he will soon declare the Strait of Hormuz a US territory. But a presidential announcement cannot, by itself, transfer sovereignty over a waterway that lies between Iran and Oman and is governed by a complex set of rules on territorial waters and passage.

Trump made the claim on Friday as Washington and Tehran remain locked in a military and diplomatic standoff over the strait, through which a fifth of global oil and gas passes. Iran has blocked the passage to leverage it as a global economy kill switch, while Washington has maintained a military naval blockade against Iran's ports, choking its economy further.

The remarks also come as the memorandum of understanding signed between the US and Iran in June expires on Sunday. The two sides remain caught in a contest over the waterway, with Tehran demanding US concessions for its reopening and Washington maintaining pressure through its blockade and sanctions.

The question is whether the US has any legal basis to turn Trump's declaration into territorial control.

Why the geography of Hormuz matters

The geography of the Strait of Hormuz makes Trump's proposal difficult to reconcile with existing international law.

The strait lies between Iran and Oman and, at its narrowest point, is only about 21 nautical miles, or 39km, wide. Under the UN Convention on the Law of the Sea, or UNCLOS, a coastal state's territorial sea extends up to 12 nautical miles, or 22km.

That means the territorial seas of Iran and Oman overlap across the strait.

UNCLOS also recognises a right of passage for ships through international straits, which "shall not be impeded".

Neither the US nor Iran has ratified UNCLOS. However, its rules on international straits are widely regarded as customary international law.

The legal position is therefore more complicated than saying that Iran has complete sovereignty over the entire waterway. Iran has sovereignty over territorial waters near its own coast, while Oman has territorial waters on its side. Even Iran does not enjoy unfettered sovereignty over the strait as a whole.

“It’s clear the US president, with a chuckle as he said that, even himself, is not taking this particularly seriously,” said Al Jazeera’s Kimberly Halkett, reporting from Washington, DC.

“These are the territorial waters of Iran and Oman. But what the US president likes to do is get under the skin of adversaries, and, in this case, it’s Iran,” she said.

That does not, however, settle the separate question of the US naval blockade, which remains in effect.

What would it take for the US to annex the territory?

Trump cannot acquire the Strait of Hormuz simply by declaring it American territory.

Bruce Fein, associate deputy attorney general under President Ronald Reagan, says Trump is constitutionally powerless to annex on his own.

“A treaty ratified by the Senate or statute is constitutionally required to annex territory, as with the Louisiana Purchase or annexation of Hawaii or Panama Canal or acquisition of Puerto Rico or the Philippines in ending the Spanish-American War.

If he goes ahead with annexation, Fein says, it would “constitute the crime of aggressive war under international law, including the UN Charter”.”

International law presents another obstacle.

Natalie Klein, a specialist in international law and associate dean at the University of New South Wales, Sydney, said, “Essentially the only way Trump’s claim could have any plausibility under international law would be if the US was asserting control over the Strait as an occupying power perhaps comparable to the authority the US exercised over Japan immediately after World War II.”

“But in that scenario, the US would need to have military control over Iran or at least its coastal areas.”

The existing US naval blockade does not, by itself, change the territorial status of the strait.

Trump has made other territorial threats during the war. He had earlier threatened to send US boots to Iran's Kharg Island to take over the key Iranian oil export hub. Tehran then responded by saying that its Islamic Revolutionary Guard Corps would be waiting for them, “with fingers on the trigger”.

Trump had previously also threatened to take over Greenland, an autonomous territory of Denmark.

Why does the Strait of Hormuz matter in the current standoff?

Trump's latest threat comes as control over movement through the strait remains central to the confrontation.

On Friday, Trump said: “We have the blockade. No ships get through unless we want them to,” he said.

Iran maintains that it controls the waterway. But despite the US claims, some vessels have transited the passage despite the blockade, maritime navigation data shows.

Al Jazeera has reported that the US naval blockade remains in effect. Halkett also stressed that the blockade is something Trump has not backed down from.

“What we should point out, though, is what the US president is not backing down on is the fact that there is a naval blockade by the United States in effect in the Strait of Hormuz, and that is ongoing.”

Iran, meanwhile, has been holding talks with Oman, the only other coastal country in the strait, over the management of maritime traffic.

Foreign Minister Abbas Araghchi, in comments carried by the Iranian Students’ News Agency, said negotiations between Tehran and Muscat “may reach a conclusion soon”.

But reopening the waterway is a separate issue, Araghchi said. Washington has to adhere to promises made in the June memorandum of understanding, including removal of the naval blockade and sanctions on Iran.

That is the new Iranian position on the ongoing war, where Tehran is now seeking these US concessions for mere reopening of the waterway, which were originally conditions for ending the war.

Iranian officials have also rejected Trump's territorial claim.

The head of the judiciary came out with furious rhetoric, calling the US president criminal and feather-headed, his remarks “nonsense” and saying the Strait of Hormuz belongs to Iran.

Kazem Gharibabadi, Iran’s deputy foreign minister, also responded, saying, “The Strait of Hormuz cannot be seized by tweet, nor by aircraft carrier, nor by issuing an order, nor by an election speech.”

“The Strait of Hormuz has been Iranian, is Iranian, and will remain Iranian; this strait will only be closed and opened under Iran’s command, and as long as you do not accept the reality of defeat and cease your fanciful delusions, Iran will continue to enforce the blockade,” he added.

What does the threat reveal about the wider war?

Trump's remarks come against the backdrop of a war that began on February 28 and has repeatedly seen the US president threaten military action against Iran before pulling back at the eleventh hour.

Trump has also said negotiating with Iran “is like chess”.

The conflict is creating pressure inside the US as Trump and his fellow Republicans seek to defend their narrow congressional majorities in November's midterm elections. Barely 35 percent of Americans approve of the war, according to a Reuters/Ipsos poll.

Several US media publications have reported that Washington is running short on munitions, including the crucial Patriot antimissile interceptor. Petrol prices have also increased and are now averaging more than $4 a gallon.

Last week, US Vice President JD Vance said the Trump administration’s top priority in the war was to control increasing petrol prices, while stopping Iran’s supposed race to a nuclear weapon now comes second.

Iran has also attacked its neighbours in the Gulf. Analysts say those attacks are aimed at forcing the regional countries to push Washington into a corner at the negotiating table.

Paul Musgrave, an associate professor of government at Georgetown University in Qatar, said Trump usually makes such statements primarily to speak to a US audience, especially his support base.

It is important to remember, he added, that Trump is a product of US reality TV and is, at the end of the day, a “showman”.

“This is a guy who speaks big. You have to take him seriously in some cases but not literally,” Musgrave cautioned.

Trump cannot be taken seriously, especially in this case because making the strait US territory is physically and legally impossible, he said. But the statements do show that Trump is determined not to back down from Iran and accept defeat in the months-long war, he added.

Al Jazeera's Kimberly Halkett also pointed to the continuing US naval blockade, despite Trump's remarks about the strait's status.

So, can Trump actually make the Strait of Hormuz US territory?

Not through a presidential proclamation alone.

US constitutional requirements would apply to any annexation, while international law provides no straightforward basis for Washington to claim sovereignty over the Strait of Hormuz. The strait lies between Iran and Oman, and even the existing US naval blockade does not itself transfer territorial sovereignty to the United States.

Trump can announce that intention, but the announcement itself would not change the legal status of the Strait of Hormuz.