The US has issued a new advisory on Monday to commercial vessels transiting the Strait of Hormuz and Gulf of Oman, advising American-flagged ships to remain as far as possible from Iranian waters without compromising navigational safety.

Iran has in the past threatened to close down the Strait of Hormuz and has at times seized commercial ships and oil tankers moving through the area alleging smuggling.

The U.S. Department of Transportation’s Maritime Administration cited a continuing pattern of Iranian boardings and seizures.

Iranian forces historically have utilized small boats and helicopters during boarding operations and have attempted to force commercial vessels into Iranian territorial waters, including as recently as Feb. 3, the U.S. Maritime Administration (MARAD) said in a maritime advisory on Monday.

“It is recommended that U.S.-flagged commercial vessels transiting these waters remain as far as possible from Iran’s territorial sea without compromising navigational safety. When transiting eastbound in the Strait of Hormuz, it is recommended that vessels transit close to Oman’s territorial sea,” according to the guidance posted on its website.

It also said crews should not forcibly resist Iranian forces if they board: “If Iranian forces board a U.S.-flagged commercial vessel, the crew should not forcibly resist the boarding party. Refraining from forcible resistance does not imply consent or agreement to that boarding.”

“If Iranian forces seek to board a U.S.-flagged commercial vessel navigating these waters, the vessel’s Master should, if the safety of the ship and crew would not be compromised, decline permission to board, noting that the vessel is proceeding in accordance with international law, as reflected in the Law of the Sea Convention,” it added.

Officials recommended U.S.-flagged commercial vessels to transit these waters with their Automatic Identification System (AIS) transponders on unless specifically advised otherwise by NAVCENT NCAGS. As disclosed, some vessel seizures by Iranian forces were claimed to be a result of vessels not transmitting on AIS.

The advisory urged U.S.-flagged commercial vessels operating in these waters to conduct a pre-voyage risk assessment, incorporate appropriate protective measures into vessel security plans, exercise caution, and monitor VHF Channel 16.

Under the guidance, ships are advised – in the event of any incident – to activate the Ship Security Alert System, contact the U.S. Fifth Fleet Battle Watch and the United Kingdom Maritime Trade Office (UKMTO).

The advisory, which supersedes and cancels U.S. Maritime Advisory 2025-009, will remain in effect until August 8, 2026.

The warning comes as tensions remain high between Washington and Iran over Tehran’s nuclear programme.

While both sides have indicated readiness to revive diplomacy over Tehran’s long-running nuclear dispute with the West, US ratcheted up the pressure on Iran last week with a fresh round of sanctions targeting 15 entities, two individuals, and 14 vessels.

The sanctions announcement came as Iran and the United States held indirect talks on Friday, an effort that appeared to reset discussions over Tehran’s nuclear programme.

Iran’s foreign minister Seyed Abbas Araghchi after the conclusion of nuclear talks in Muscat said the “viewpoints were conveyed” and “our concerns were expressed.”

“It was a good start” the minister noted, but its continuation, he said, “depends on consultations in our respective capitals and deciding on how to proceed.”

Araghchi stressed that there was a “consensus” that the negotiations would continue.