The United States says it is starting a blockade of all maritime traffic at Iranian ports in the Strait of Hormuz, ratcheting up tensions in the region after Iran and the United States failed to reach a peace deal over the weekend.

A central sticking point in the nations’ marathon negotiations in Islamabad on Saturday, April 11, was the United States demand to reopen the strait, a narrow waterway that has become Iran’s most effective tool in the joint war launched by the United States and Israel more than seven weeks ago.

The 100-mile-long waterway connects the Persian Gulf with the Gulf of Oman and the Arabian Sea, bordered on one side by a swath of Iranian coastline. Before the war, roughly 20% of the world’s oil and natural gas supply passed through the narrow channel. But since Iran has effectively closed the passage in response to the joint U.S.-Israel strikes beginning on Feb. 28, shipping has been at a virtual standstill. Its closure has left hundreds of tankers in the Gulf unable to enter or leave through the strait. It has roiled global markets and led to a surge in global energy prices.

US to blockade Iranian ports, oil prices surge.

A U.S. official told USA TODAY on April 12 that the negotiations fell apart over multiple issues, including how to address Iran’s nuclear program and facilities, its support for Hamas and Hezbollah and demands by the United States that Iran reopen the strait and not impose tolls.

Several hours after the talks fell apart, President Donald Trump announced on social media early April 12 that the U.S. Navy would impose a blockade on the Strait of Hormuz.

Here is what to know.

Where is the US Navy implementing the blockade?
The parameters of the blockade have changed significantly since the president first announced it on April 12, from a complete lockdown of the strait to a more targeted operation focused on Iranian ports.

“Effective immediately, the United States Navy, the Finest in the World, will begin the process of BLOCKADING any and all Ships trying to enter, or leave, the Strait of Hormuz,” Trump said in his first announcement on Truth Social.

President Donald Trump arrives at the White House in Washington, D.C., U.S., April 12, 2026.
In an interview with Fox News’ “Sunday Morning Futures” about an hour after his social media posts, Trump called the operation a “complete blockade.” When asked what he was trying to accomplish, Trump said he was aiming to reopen the strait for all ships, calling it an “all in and all out.”

The U.S. Central Command later said that the blockade, which is slated to begin at 10 a.m. ET, would be more targeted.

The blockade will be “enforced impartially against vessels of all nations entering or departing Iranian ports and coastal areas,” U.S. Central Command said, including from “all Iranian ports on the Arabian Gulf and Gulf of Oman.”

More: US-Iran ceasefire hinges on Strait of Hormuz. Why is it so important?
In a note to seafarers seen by Reuters, U.S. Central Command said the blockade would apply to all vessel traffic regardless of their flag along the Iranian coastline in the Gulf of Oman and Arabian Sea, east of the Strait of Hormuz.

The area amounts to roughly 21,000 square miles along the Iranian coastline, a space roughly 87% the size of West Virginia.

The note said any vessels departing the blockaded area would be subject to “interception, diversion, and capture,” but vessels passing through the strait to or from non-Iranian destinations would not be affected, Reuters reported. It also said that humanitarian shipments, including food, medical supplies and other essential goods, would be permitted within the blockade but would be subject to inspection.

Will other nations join in the blockade?
The president also said in the 30-minute Fox News interview over the weekend that “numerous countries” would be helping with the blockade, but did not specify which nations would assist and how. He suggested the United Kingdom could help with clearing mines Iran placed in the strait, though the country’s prime minister later stated his government would not assist in implementing the blockade.

British Prime Minister Keir Starmer on April 13 said in an interview with the BBC that his country was “not supporting” Trump’s threatened blockade, and that the United Kingdom is “not getting dragged into the war.”

He added that it’s vital that “we get the strait open and fully open,” and announced there would be a summit this week jointly with France to advance a plan .

Israeli Prime Minister Benjamin Netanyahu on April 13 said he supports Trump’s blockade plan for the strait, saying: “We, of course, support this aggressive stance, and we are coordinating with the United States all the time.”

Why is the US imposing a blockade?
The blockade is designed to increase economic pressure on Iran to open the strait and reach an agreement to end the conflict, several experts said.

Robin Brooks, a senior fellow at the Brookings Institution, has argued that a blockade exerts financial pressure on the regime dependent on oil exports and avoids more potential loss of life if the United States and Israel tried to seize Kharg Island, Iran’s main oil export terminal.

“A blockade collapses Iran’s imports to zero because there’s no cash from oil exports to pay for anything. It sends Iran’s currency into a devaluation spiral and the economy into hyperinflation,” he said on X.

At the same time, he said, the strategy’s risks include rising oil prices and potential fallout in U.S. financial markets.

Karen Young, a senior research scholar at Columbia University’s Center on Global Energy Policy, told USA TODAY that while a blockade would cause financial distress in Iran, that does not necessarily mean it will change the country’s negotiating positions as the strategy pushes up oil prices. It also might lengthen the time it takes to open the strait completely.

“Iran has long shown an ability to weather economic pressure, and sees little reason to alleviate the consequences for its citizens,” Young said.

James Stavridis, a retired U.S. admiral and former NATO Supreme Allied Commander, told CNN the blockade would require one or two aircraft carriers, a dozen surface ships stationed off the ports and a couple dozen smaller boats in what would be a “resource-intensive” strategy.

While Iran could still respond by adding more mines to the strait or going after Gulf states oil infrastructure, Stavridis noted on social media that, “In recent days the ONLY people benefiting from Gulf transit were the Iranians.”

Global leaders respond as the U.S. blocks the Strait of Hormuz with Iran vowing retailation, sending oil prices higher and dropping markets shares.
“With a blockade…their economy will be choked…and the US and our allies are no worse off than we were after the Iranians started holding the Strait hostage,” he wrote.

Emory University law professor and former Navy lawyer Mark Nevitt flagged his April 13 analysis, highlighting that reopening a critical strait, which accounts for 11% of global maritime trade, won’t happen swiftly even if an agreement is reached. That’s partly because Iran mined the area.

“New reporting suggests that Iran mined the Strait haphazardly, failed to record mine locations, and lacks the capacity to conduct effective clearance operations,” he wrote. “Until those mines are found and removed, the Strait is practically closed.”

The Callisto tanker sits anchored as the traffic is down in the Strait of Hormuz, amid the U.S.-Israeli conflict with Iran, in Muscat, Oman, March 10, 2026.
How has Iran responded?
Iran has issued its own threats in response to the impending blockade, warning it would violate the tenuous two-week ceasefire that began on April 7, and indicating it could once again begin targeting the United States’ allies in the Gulf.

Iran’s Revolutionary Guard Corps said in a statement to Iranian state media on April 12 that any military vessels attempting to approach the strait would be considered in violation of the two-week ceasefire and would be dealt with harshly and decisively.

Iranian military spokesperson Ebrahim Zolfaghari warned on April 13 that if Iran’s ports are threatened, no ports in the Gulf or the Gulf of Oman would remain secure. He added that any blockade of vessels in international waters would amount to “piracy,” according to Iranian state media.

Contributing: George Petras, USA TODAY.

This story has been updated

Source: USA TODAY.