The warning issued by the US Navy shortly before the blockade on Iran's ports came into force

The US military has warned that any ship entering or leaving the soon-to-be blockade zone without permission will be “subject to interception, diversion and capture”, Sky News and The Guardian report.

The US military will impose a blockade in the Gulf of Oman and the Arabian Sea east of the Strait of Hormuz, which will apply to all naval traffic, regardless of flag, US Central Command said in a memo to mariners seen by Reuters on Monday.

The note states that the blockade will come into effect on Monday at 14:00 GMT (17:00 Romanian time).

“Any vessel entering or leaving the embargoed area without authorization is liable to interception, diversion and capture,” US Central Command warned.

“The blockade will not prevent neutral transit through the Strait of Hormuz to or from non-Iranian destinations,” the US military said.

The blockade “comprises the entire Iranian coastline, including but not limited to ports and oil terminals,” the memo said, adding that humanitarian shipments, including food, medical supplies and other essential goods, would be allowed, subject to inspection.

US President Donald Trump initially announced on social media that the US Navy would prevent “all without exception” ships from passing through the Strait of Hormuz, but the US military later said it would apply the blockade “impartially” to ships entering and leaving Iranian ports.

Tehran has threatened to retaliate against its Gulf neighbors' ports after talks over the weekend failed to reach an agreement to end the war, putting the ceasefire at risk.

Iran's military threatens: “No port in the Persian Gulf and the Arabian Sea will be safe anymore”

Also on Monday, Iran's military said the US naval blockade, due to begin later, was “illegal” and an act of piracy, while warning that no Gulf port would be safe if its ports were threatened, AFP reported.

“The restrictions imposed by the criminal America on maritime navigation and transit in international waters are illegal and constitute an example of piracy,” the command of Iran's armed forces, Khatam Al-Anbiya, said in a statement read on state television.

“If the security of the Islamic Republic's ports in the waters of the Persian Gulf and the Arabian Sea is threatened, no port in the Persian Gulf and the Arabian Sea will be safe,” the Iranian command added, according to Agerpres.

Large-scale military operation

A naval blockade imposed on Iran by the US is a major, indefinite military action that could trigger further retaliation from Tehran and put enormous pressure on an already fragile truce, experts consulted by Reuters say.

The ultimate goal of the operation, Trump said, would be to pressure Iran to end the effective closure of the Strait of Hormuz, a narrow but essential waterway for about 20 percent of the world's oil. All countries were affected by the closure of the Strait of Hormuz, except for those that ensure safe passage from Tehran.

If Trump's strategy is successful, it would remove the biggest leverage Iran has in negotiations with the United States and reopen the strait to global trade, which could lead to lower oil prices.

But, according to the experts consulted by the international press agency, a blockade is an act of war that requires an unlimited commitment of a significant number of warships, notes News.ro.

“Trump wants a quick fix. The reality is that this mission is difficult to execute alone and probably unsustainable in the medium to long term,” said Dana Stroul, a former senior Pentagon official during the Biden administration who now works at the Washington Institute for Near East Policy.

The US military has yet to provide basic details about the blockade, including how many US warships will enforce it, whether fighter jets will be used and whether any Gulf allies will contribute to the effort. Central Command declined to respond to requests for comment.

With enough warships, the US Navy could set up a blockade that would intimidate many commercial tankers, preventing them from trying to get through with Iranian oil, experts say.

But would the United States be prepared to board and seize—or even damage or sink—ships trying to break the blockade? What if they were transporting oil for China, a major power, or US partners like India or South Korea? And what would Iran do?

Rear Admiral Gary Roughead, former head of US naval operations, warned that Iran could fire on ships in the Gulf or attack the infrastructure of Gulf states that host US forces.

“Honestly, I think if we start doing that, Iran will have some reaction,” Roughead said.

Iran's threats to shipping have caused global oil prices to soar by about 50% since the US and Israel went to war on February 28.

On Sunday, Trump said the price of oil and gasoline could remain high in the United States until the midterm elections in November, which could lead to Trump's Republicans losing control of the US Congress if there is a negative public reaction. War is already unpopular.

Gasoline price problem

Frustrated by Iran's refusal to end the war on his terms, Trump on Sunday also hinted at the possibility of resuming US strikes inside Iran, citing missile factories as a possibility.

US Sen. Mark Warner of Virginia, the top Democrat on the Senate Intelligence Committee, questioned the strategy, saying Iran could send fast boats to mine the strait or plant bombs against oil tankers.

“How could this ever lower gas prices?” Warner asked on CBS' “Face the Nation.”

Thousands of US military strikes have severely weakened the Iranian military. But analysts say Tehran has emerged from the conflict as a vexing problem for Washington, with more intransigent leadership and a hidden stockpile of highly enriched uranium.

Also on Sunday, Trump threatened that any Iranian who fires at the ships “will be THROWN TO HELL!”

Iran's Revolutionary Guards responded with a statement warning that military vessels approaching the strait would be considered a violation of the ceasefire and dealt with harshly and decisively, indicating the risk of a dangerous escalation.

Dana Stroul said that solving the crisis will require a long-term international effort. “In the long term, this problem will have to be solved through diplomacy and international political will”, she emphasized.