United States President Donald Trump’s threat to begin blocking the Strait of Hormuz immediately after talks in Islamabad between Washington and Tehran ended without an agreement is a significant escalation in the war on Iran, analysts say.
In a social media post on Sunday, Trump said the US Navy would “begin the process of interdicting any and all vessels attempting to enter or leave the Strait of Hormuz”.
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Trump’s comments raised concerns about the status of a two-week ceasefire announced last week between the US and Iran.
Chris Featherstone, a political scientist at the University of York, told Al Jazeera that Trump’s threat to block the Strait of Hormuz is “absolutely an escalation” in the US and Israel’s war on Iran.
He said, “Trump is using the threat of a blockade as a tool in negotiations with Iran. Trump has said Iran has no cards, and this attempt to leverage the blockade on Iran would be an attempt to put further pressure on Iran to adhere to US goals in the negotiations.”
What might a blockade look like? Here’s what we know:
What kind of blockade is the US threatening?
Shortly after the US and Israel launched attacks on Iran on February 28, Iran essentially took control of the Strait of Hormuz, a key choke point for global energy markets. Before the war began, 20 percent of the world’s oil and liquefied natural gas (LNG) supplies were shipped through the strait.
After a Pakistan-brokered ceasefire came into effect on Wednesday, Tehran confirmed it would allow shipping through the Strait of Hormuz for the duration of the two-week agreement, reducing the disruption that had sent global oil and gas prices soaring.
However, it is unclear whether Iran is collecting fees for the passage during the ceasefire. During the war, only certain ships from specific countries considered friendly to Iran and those that paid tolls were granted safe passage.
After weekend talks in Pakistan ended without any agreement, Trump threatened to block the Strait of Hormuz and also accused Iran of “extortion”. He said the US Navy would detect and interdict ships in international waters that have paid Iran tolls to transit the strait.
Later, the US military said it would block all maritime traffic entering and exiting Iranian ports, including the Gulf and the Gulf of Oman. The blockade is scheduled to begin at 10 a.m. Monday, Washington, DC, time (14:00 GMT).
US military Central Command (CENTCOM), which has responsibility for operations in the Middle East, told Reuters news agency that US forces will enforce the blockade in the Gulf of Oman and the Arabian Sea east of the Strait of Hormuz and it will apply to all ships regardless of flag.
It states, “Any vessel entering or departing a blocked area without permission is subject to interception, diversion and capture.”
“The blockade will not disrupt neutral transit routes through the Strait of Hormuz or to non-Iranian destinations.”
However, Iran’s armed forces said that the US “imposing restrictions on the movement of ships in international waters is an illegal act and tantamount to piracy”.
Jason Chua, a professor of maritime law at City St George’s, University of London and the Maritime Institute of Malaysia, told Al Jazeera that Washington’s action would not be a classic blockade, but a case of “an embargo on warships on the orders of President Trump”.
“This would amount to a steady pattern of stopping, boarding and seizing ships deemed linked to Iran, essentially imposing sanctions at sea,” he said.
Is this legal under international maritime law?
Chua said the legality of such a blockade by the US is “difficult”.
“The United States is not a party to the UN Convention on the Law of the Sea, but that does not mean it is free to impose a blockade as it sees fit,” he said. “The basic rules regarding freedom of navigation and passage through major waterways are widely accepted as customary international law, so they bind states whether they have signed the treaty or not.”
He added: “Now, if you want to legally call something a blockade, you are really in the area of ​​the law of armed conflict at sea – think of the San Remo Manual on International Law applicable to armed conflicts at sea. However, that assumes that you are in an actual armed conflict, that you have declared a blockade, that it is effective and that it is equally applicable to neutral ships. That framework sets a high legality bar for a blockade.”
Chua said that even if Trump uses sanctions as justification for Washington’s actions regarding Iranian ports, it does not fully resolve the legal issues.
“Even fairly strong domestic sanctions do not automatically give you the right under international law to intercept foreign ships on the high seas without UN Security Council consent or support. At best, sanctions can justify why you act but not always where you can act,” he said.
Will other countries join the US in the blockade?
So far, only the United Kingdom has clearly stated that it will not join Trump’s blockade of Iranian ports.
In an interview with BBC 5 Live on Monday, British Prime Minister Keir Starmer said he is focused on reopening the Strait of Hormuz “as quickly as possible” to reduce global energy prices.
He said, “We are not supporting the blockade, and are not supporting all the marshaling diplomatic, political and capacity… From our perspective, it is all focused on completely opening the strait.”
Meanwhile, China has urged peace from all sides.
Foreign Ministry spokesman Guo Jiaqun said that maintaining the vital waterways safe, stable and unobstructed serves the common interests of the international community. He said China is ready to work with all parties to ensure energy security and security of supply.
Featherstone said that one of the most striking features of the US-Israeli war on Iran is that many US allies, such as Britain, are unwilling to get involved.
He said, “Given that this blockade would take place in the middle of armistice negotiations, which would risk breaking down the talks, it is unlikely that any ally would want to get involved now.”
He said, “As with other elements of this war, the (US) administration has not outlined the purpose of this potential blockade. US allies would likely want to know the purpose of the blockade before committing and risking retaliation.”
How could the US blockade harm Iran?
Even though Iran has become accustomed to US sanctions and has been operating even during the war, such a blockade could cause greater damage to Iran’s economy.
The Unified Command of the Iranian Armed Forces said ports in the Gulf and the Sea of ​​Oman are “either for all or for no one”, state broadcaster IRIB reported.
“The Armed Forces of the Islamic Republic of Iran consider it a natural and legal duty to defend the legal rights of our country and, accordingly, exercising the sovereignty of the Islamic Republic of Iran in the territorial waters of our country is the natural right of the Iranian nation,” the IRIB quoted Iran’s military as saying.
The statement said “ships belonging to the enemy” would not have the right to pass through the Strait of Hormuz, while other ships would be allowed to pass subject to Tehran’s regulations.
“The imposition of a criminal US ban on the movement of ships in international waters is an illegal act and tantamount to piracy.”
The statement said no port in the region “will be safe” if the security of ports is threatened.
Reporting from Doha, Qatar, Al Jazeera’s diplomatic editor James Baze said Washington’s blockade could seek to hurt the Iranian economy, which is performing well despite the war, by continuing to send its oil supplies through the Strait of Hormuz.
“It’s almost a race to damage the economy of Iran, a country that has been under sanctions since 1979 and that is very resilient economically even though it has deep economic problems,” he said.
Featherstone said Iran has become accustomed to US dominance over its economy.
“Iran has experienced heavy US sanctions for decades, and for most of that time, the US sanctions regime has prevented any country that trades with the US from doing business with Iran,” he said.
“However, given the extent of US and Israeli attacks on Iran, this will impact their ability to rebuild,” he said.
What will happen to the Iranian mines in the strait?
On Wednesday, the Islamic Revolutionary Guard Corps (IRGC) released a map of the Strait of Hormuz, showing a safe route for ships to pass through the strait, avoiding the mines laid along it.
The map appears to direct ships north towards the Iranian coast and away from the traditional route near the coast of Oman.
In a statement, the IRGC said all vessels should use the new map for navigation due to “the possibility of the presence of various types of anti-ship mines in the main traffic area.”
In his Truth Social post on Sunday about the blockade of the Strait of Hormuz, Trump said US forces would begin clearing mines that Iran has placed in the Strait and said NATO countries like Britain would help in the process.
But on Monday, Starmer told BBC 5 Live that although the UK had “minesweeping” capabilities, it would not get involved in “operational matters”.
Meanwhile, Japan said it had not yet decided whether to deploy its Self-Defense Forces for a mine clearance operation in the Strait of Hormuz.
Chief Cabinet Secretary Minoru Kihara told reporters that Japan is urging progress toward a comprehensive understanding between the US and Iran.
“The most important thing is that de-escalation, including ensuring the safety of navigation through the Strait of Hormuz, has indeed been achieved,” Kihara said, according to Kyodo news agency.
What does Trump’s blockade mean for shipping in the strait?
During the US–Israeli war over Iran, Tehran allowed the passage of a small number of ships from countries it considers “friendly nations”, such as India, China, Japan, Turkey and Pakistan.
Some ships that also paid tolls to Iran were allowed to pass. At least two of the tolls for the vessels are believed to have been paid in Chinese yuan, in what appears to be a strategy to weaken the US dollar and avoid US sanctions. China, which buys 80 percent of Iran’s oil, already pays Tehran in yuan.
On Friday, Iran said it was considering a proposal to collect tolls in its currency, the rial, in the future.
Chua told Al Jazeera that Washington’s blockade of Iranian ports would sharply impact shipping from Indian, Chinese, Japanese, Turkish and other countries.
“You don’t have to be Iranian to get caught up in this (the blockade). If there is an Iranian link in the cargo, financing or ownership chain, you are suddenly in the risk zone,” he said.
He warned that insurance premiums were likely to rise, which would make global banks nervous. The global tanker market will also begin to segment into different risk levels, he said.
“The moment the conflict starts, neutral shipping starts to feel a lot less neutral,” he said.
He said that the bigger picture of such blockade is also worrying.
“If major powers begin to routinely stop ships based on where they are or what they are doing, rather than who they are connected to, it harms the stability of the entire system.
The real issue is not just Iran – what it does with the rules that everyone else relies on,” he said.
