New enforcement rules allow American forces to board, search, and detain suspected Iranian-linked ships worldwide, raising risks of escalation and retaliation across key maritime routes
The United States has significantly broadened its naval blockade on Iran, signaling that vessels linked to Tehran can now be boarded, searched, and seized on the high seas worldwide under wartime enforcement authorities, according to Pentagon leadership and a maritime advisory issued to commercial shipping.
The update, released on April 16 through a Joint Maritime Information Center (JMIC) note citing U.S. Naval Forces Central Command, states that “all Iranian vessels, vessels with active OFAC sanctions, and vessels suspected of carrying contraband … are subject to visit, board, search, and seizure,” regardless of location.
The revised guidance marks a major expansion from the original blockade announced on April 13, which focused on vessels entering or leaving Iranian ports and coastal facilities after U.S.–Iran negotiations failed to produce a breakthrough.
Central to the expansion is a broad definition of contraband that extends beyond weapons and military systems to include a wide range of dual-use goods—items with both civilian and military applications.
Broad Definition of Contraband
According to the advisory, “absolute contraband” includes weapons, ammunition, military vehicles, and specialized systems. It also classifies “conditional contraband” such as petroleum, industrial materials, machinery, electronics, and communications equipment when destined for Iran and deemed supportive of its military or war-sustaining economy.
The scope suggests the expanded enforcement could affect cargo flows beyond energy shipments, including goods traded by third countries with Iran, if U.S. officials determine potential military end use.
While the blockade remains centered on Iran’s coastline and surrounding waters, the updated directive invokes the “belligerent right to visit and search,” a doctrine in naval warfare law that permits interception of suspected enemy-linked shipping on the high seas.
Chairman of the Joint Chiefs of Staff Gen. Dan Caine confirmed during Thursday’s Pentagon briefing that the blockade is being enforced beyond the immediate Gulf theater, with U.S. forces prepared to pursue vessels tied to Iran across multiple operational regions.
“The joint force, through operations and activities in other areas of responsibility, like the Pacific Area of Responsibility … will pursue any Iranian-flagged vessel or any vessel attempting to provide material support to Iran,” Caine said, adding that enforcement may include direct action at sea, including boarding and seizure.
“Turn around or prepare to be boarded if you do not comply with this blockade—we will use force,” he warned, outlining escalation measures that could include warning shots and vessel takeover.
Shadow Fleet in Focus, Retaliation Risks
Analysts say the expanded rules, which also target Iran’s so-called shadow fleet—a network of more than 500 tankers used to transport oil and other cargo under sanctions—could provoke retaliation.
“Then, the ball is in Iran’s court in terms of retaliation that could include anything from boarding, ship attack, port attack and even expanding to the Red Sea,” Martin Kelly of EOS Risk Group wrote in a post on X on Thursday.
Iran has previously warned it could target regional ports in response to the blockade and potentially disrupt all import and export traffic across the Red Sea, the Gulf of Oman, and the Persian Gulf.
The Strait of Hormuz, which carries roughly one-fifth of global oil and liquefied natural gas flows, remains a focal point of the crisis, with Iranian forces tightening control over vessel movements in response to the U.S.–Israeli military campaign.
U.S. Forces Prepare for Sustained Operations
At the same Pentagon briefing, the head of U.S. Central Command, Adm. Brad Cooper, said American forces are using the cease-fire period to prepare for extended operations should hostilities resume.
“We’re rearming, we’re retooling, and we’re adjusting our tactics, techniques, and procedures. There’s no military in the world that adjusts like we do, and that’s exactly what we’re doing right now during the ceasefire,” Cooper said.
He described U.S. forces operating at more than 70 locations across the Middle East, working with regional partners and integrating new technologies, including artificial intelligence and drone systems, into planning.
“I met with teams who launched our own one-way attack drones into Iran,” Cooper said. “These were originally Iranian-designed drones. We brought them back to America, took the guts out, put a ‘Made-in-America’ stamp on them, and fired them right back to Iran. Very effective.”
Hostilities could resume if the two-week cease-fire announced by U.S. President Donald Trump on April 7 expires without progress in negotiations.
The Trump administration has expressed optimism about reaching a diplomatic resolution. White House press secretary Karoline Leavitt said Wednesday that discussions toward a peace agreement are “productive and ongoing.”
“We feel good about the prospects of a deal,” she said.
During Thursday’s briefing, Secretary of War Pete Hegseth urged Iranian leaders to accept the proposed deal.
“We’d prefer to do it the nice way, through a deal led by our great vice president and negotiating team, or we can do it the hard way,” he said. “We urge this new regime to choose wisely.”
