ISTANBUL

The US Department of Transportation's Maritime Administration issued an advisory Monday warning American-flagged commercial vessels to avoid Iranian territorial waters in the Persian Gulf region.

"It is recommended that US-flagged commercial vessels transiting these waters remain as far as possible from Iran's territorial sea without compromising navigational safety," the advisory noted, effective through Aug. 8.

The guidance recommends that eastbound vessels in the Strait of Hormuz "transit close to Oman's territorial sea" to minimize risk.

"Commercial vessels transiting the Strait of Hormuz and Gulf of Oman have long been at risk of being hailed, queried, boarded, detained, or seized by Iranian forces," the Maritime Administration said.

If hailed by Iranian forces, vessels should provide their name and flag state while affirming they are proceeding under international law, the guidance states.

Masters should decline boarding permission if safe to do so, noting compliance with the Law of the Sea Convention, though crews should not forcibly resist if boarding occurs, the advisory added.

The Maritime Administration recommended vessels keep Automatic Identification System (AIS) transponders on, as "some vessel seizures by Iranian forces were claimed to be a result of vessels not transmitting on AIS."

The advisory comes as Washington significantly increases its military presence in the region amid heightened tensions with Tehran.