Explained | Why and how US blockading Iranian ports in Strait of Hormuz

Despite the US blocking, maritime tracking firm Kpler indicated on Tuesday that at least two vessels successfully passed through the strait on Monday.

Following the collapse of peace negotiations between Iran and the United States in Islamabad last week, Washington announced that it had started restricting vessels from entering or leaving Iranian ports via the Strait of Hormuz on Monday.

As the blockade came into force that morning, President Donald Trump issued a stark warning: “If any of these ships come anywhere close to our BLOCKADE, they will be immediately ELIMINATED, using the same system of kill that we use against the drug dealers on boats at Sea,” he wrote on Truth Social, adding, “It is quick and brutal.” He further stated that the restriction applies to “any and all Ships trying to enter, or leave, the Strait of Hormuz.”

Despite these measures, maritime tracking firm Kpler indicated on Tuesday that at least two vessels successfully passed through the strait on Monday.

Here, the article explores why and how Trump has blocked Iranian ports. 

Why did Trump decide to block Hormuz?

Trump has described the blockade as a way to intensify pressure on Iran and force it to reopen the vital oil transit route. “We can’t let a country blackmail or extort the world, because that’s what they’re doing,” he told reporters outside the Oval Office after the action began.

In an interview with Fox News, he added that "we're not going to let Iran make money on selling oil to people that they like and not people that they don't like", emphasizing an “all or nothing” approach to access through the channel. Iran, however, has condemned the move as “piracy” and warned it could respond by targeting Gulf state ports.

The Strait of Hormuz had already been disrupted by Iran during the ongoing conflict, reducing oil flows and driving global prices upward. The US action seeks to reverse that situation by cutting Iran off from international trade, limiting both imports and the oil revenues that support its government, reported The New York Times.

Wall Street Journal report said that Trump pitched to block the Hormuz as a opportunity for American oil-and-gas exporters. It added that the blockade could cut off nearly 2 million barrels of oil that Iran has continued to ship through Hormuz. 

Robin Brooks, a senior fellow at the Brookings Institution, argues that imposing a blockade would financially strain a regime that is heavily reliant on oil exports, while avoiding the greater loss of life that could result if the United States and Israel attempted to seize Kharg Island.

Where is the blockade?

The precise positioning of US naval forces has not been publicly disclosed, However, guidance issued to mariners, seen by Reuters indicates the restrictions apply to vessel traffic along Iran’s coastline in the Gulf of Oman and the Arabian Sea, east of the Strait of Hormuz.

The note said ships leaving the restricted zone may face “interception, diversion, and capture,” while vessels merely transiting the strait to non-Iranian destinations are not expected to be targeted, added Reuters report. It also said that humanitarian cargo, including food and medical supplies, is allowed but subject to inspection.

The covered maritime area spans roughly 21,000 square miles along Iran’s coast, according to USA Today. Satellite imagery from April 11, as reported by BBC Verify, shows the USS Abraham Lincoln positioned near the eastern Gulf of Oman, about 200 km south of Iran. Additional nearby vessels appear consistent with guided-missile destroyers likely accompanying the carrier strike group.

US Central Command (CENTCOM) has said more than 12 warships and more than 100 fighter and surveillance aircraft are involved in the blockade.

How is the blockade being implemented?

Details of enforcement remain limited. US began mine-clearing efforts over the weekend and CENTCOM's commander, Admiral Brad Cooper, said US forces would begin the "process of establishing a new passage... to encourage the free flow of commerce", Sky News reported.

Trump has also said US forces will neutralize naval mines he claims Iran deployed in the strait, adding that a broader agreement on free passage could eventually be reached.

In a recent update CENTCOM said that six merchant vessels have been asked to turn around and re-enter an Iranian port in the Gulf of Oman.

Reportedly, two Iran-linked vessels that travelled through the Strait of Hormuz have now changed direction and appear to be heading back.

How will the blockade affect countries?

BBC reports that the blockade presents two major risks: one, rising global energy prices and second the possibility of renewed large-scale conflict between the US and Iran, which could also impact Gulf nations.

Mukesh Sahdev, chief oil analyst at XAnalysts, believes the US should be able to withstand higher gas and oil prices better than Iran can weather a major blow to its export income, reported Sky News.

NYT repot said that the move comes with significant risk not just for Iran but for the global economy and energy supplies, at least in the short term

Iranian officials have warned of broader economic consequences. “Enjoy the current pump figures. With the so-called ‘blockade’, Soon you’ll be nostalgic for $4–$5 gas,” parliamentary speaker Mohammad Bagher Ghalibaf said in a post on X.

The impact could extend to major Asian economies, which receive the majority of oil passing through the strait. Reportedly, a prolonged disruption could increase fuel and food prices globally while affecting access to industrial materials such as aluminum and fertiliser inputs.

The International Monetary Fund has also warned that sustained conflict and elevated energy prices could push the global economy toward recession. Iran itself may face internal strain, particularly due to its reliance on imported grain and wheat.

Is the blockade valid?

International Maritime Organization maintains that no nation has the legal authority to block transit through straits used for international navigation. Secretary-General Arsenio Dominguez stated: “I do understand there is a conflict going on there, but there is still no legal basis in international law to take any actions to block any strait used for international navigation,” added BBC report.