Iran blockade ushers in dangerous new phase of Iran war

American forces began their blockade of Iranian ports on Monday, even as allies scrambled to understand how it will work — and how the Trump administration will avoid sparking new showdowns with the move.

More than a dozen U.S. warships in the region are available to take part, according to one U.S. official, including the USS Tripoli, which has an embarked Marine unit aboard trained to interdict and board ships.

Additional details remain scarce — including how long the blockade will last and what its precise strategic goals are. But President Donald Trump said it will bar ships that have left or plan to enter Iranian ports, as well as any ships that paid Iranian tolls for safe passage.

The maneuver threatens to kick off a dangerous new phase of the war that could see U.S. troops executing high-risk boarding operations of foreign ships in the busy Persian Gulf. And it raises the possibility of wider global conflicts if the U.S. moves to stop foreign-flagged vessels, such as those from China or Russia.

Some officials questioned how U.S. military commanders will actually enforce the blockade, “especially if Iran decides to let more ships through — and not necessarily those that have paid tolls — to overwhelm the blockade," said one foreign diplomat from a nation with economic interests in the Middle East.

“Is the U.S. Navy going to interdict every one of them, and do they have enough assets for this? And how would they verify who has allegedly paid tolls?” added the diplomat, who, like others in this story, was granted anonymity to discuss sensitive issues.

At stake is the Strait of Hormuz, a vital gateway for the energy sector that Iran has effectively taken control of, causing oil prices to surge and driving up costs across the global economy. The White House appears to be betting that Tehran will capitulate and open the strait if the U.S. can cut off Iran’s ability to export its own oil via tankers.

But the passage is vital to nations well beyond Iran, including China and Japan, which import oil from ships that traverse the strait. And some countries — such as Russia — use “shadow fleet” vessels that are controlled by Moscow or Tehran, even though they are flagged under third-party nations.

While the U.S. might seize “shadow fleet” vessels, doing the same with a commercial ship hailing from China, for example, could touch off an international incident.

“If it's a flagged ship from India or a flagged ship from China that chooses to go run the blockade, or they bring a warship as an escort to protect them, now we're into a different scenario,” said John Miller, a retired three-star admiral who previously commanded American ships in U.S. Central Command. “And it remains to be seen whether we would want to force that blockade against a Chinese-flagged vessel, for example, or not.”

Beijing flatly dismissed the American blockade, and asserted its right to trade with any country it sees fit without American involvement. “Our ships are moving in and out of the waters of the Strait of Hormuz,” Chinese Defense Minister Admiral Dong Jun said in a statement Monday. “We have trade and energy agreements with Iran. We will respect and honor those agreements and expect others not to interfere in our affairs. Iran controls the Strait of Hormuz and it is open for us.”

The blockade could further expose American forces to new Iranian drone attacks, as well as fast attack boats. That means any U.S. naval presence would most likely be set up somewhere outside the relatively claustrophobic confines of the strait.

“We don't have to go up into the strait to do this,” Miller said, “because it naturally funnels itself where we can get to them before they get that far into the northern parts of the Gulf of Oman, or in the Strait of Hormuz itself.”

American vessels will likely sit at the bottom of the strait in the North Arabian Sea, where they can track maritime traffic through the area and possibly use Marines to board ships, according to Miller.

The farther those ships are off the Iranian coast, the less susceptible they might be to Iranian attack.

The U.S. military also has Coast Guard teams that are trained to board ships under the Department of Homeland Security, although it’s unclear if those units are in the region or will be deployed there.

The Pentagon pointed to a Notice to Mariners about shipping in and around the Strait on Monday when asked for comment, as well as to a statement from the U.S. Central Command Sunday announcing the blockade.

The Navy will likely direct any ships leaving or scheduled to enter an Iranian port to dock at a friendly port — most likely Duqm in Oman — which has emerged as a critical logistical hub for the U.S. Navy, according to a person familiar with U.S. military operations in the region.

The U.S. would also be responsible for taking care of the crew of detained ships in seaport, although American officials have not yet described how that process would work.

A blockade might also pose logistical challenges for the Pentagon and the Navy in particular, which is already facing significant strain from the Iran war and a separate monthslong effort to block suspected drug traffickers in the Caribbean.

For now, American allies have shown little interest in participating in the Iran blockade.

British Prime Minister Keir Starmer flatly declared on Monday that his country is “not supporting” the mission, telling the BBC that he was more focused on “bringing countries together to keep the straits open, not shut.”

Others were outright disdainful.

"Since the war began, everything has been senseless," Spain’s Defense Minister Margarita Robles told Spanish TV on Monday. "Nobody knows the reason why this war started, a war that was supposed to be quick. This is just another episode of the downward spiral we have been dragged into, and that they have tried to drag the entire world into."