Iran's seizure of the Maersk Tigris is the second time in a week it has harassed transiting vessels under U.S. protection in the Strait of Hormuz.
A senior defense official at the Pentagon said that on Friday, the Maersk Kensington, a U.S.-flagged cargo vessel, was intercepted by four Iranian Revolutionary Guard Corps Navy patrol craft.
"In the incident, the [Iranian] patrol craft at one point encircled the Maersk Kensington, and eventually followed the ship as it continued on its course. The [Iranian] units eventually withdrew from the area," the official said.
Iran's harassment of ships in the Strait follows its attempt last week to send a convoy of vessels to Yemen, which was eventually turned away after the arrival of the U.S. aircraft carrier USS Theodore Roosevelt.
The incident with the Kensington, however, differs from Tuesday's seizure of the Maersk Tigris, a Marshall Islands-flagged vessel. The Marshall Islands is a protectorate of the U.S., and dependent upon the U.S. for its defense and security.
In Tuesday's incident with the Tigris, Iranian patrol craft ordered the cargo ship — as it was transiting through a portion of the Strait controlled by Iran, but where international sea treaties have created a safe passage route — to stop its movement and turn the ship further into Iranian waters. When the shipmaster refused, the patrol craft fired warning shots across the Tigris' bow. The vessel then complied, and was boarded by Iranian forces.
Since the incident at approximately 4 a.m. Eastern time Tuesday, the Tigris has not appeared to leave the area it was last reported, near Larak, an Iranian-owned island in the Strait.
The U.S. Navy said it did not have updates on the Maersk Tigris, except that the U.S. destroyer USS Farragut is close by and monitoring the situation.
In the Maersk Kensington's case, that ship did not request assistance from U.S. Naval forces during the incident and U.S. forces were not present or involved. The Kensington's master subsequently reported the incident to U.S. Naval Forces Central Command.
In the Maersk Tigris case, the shipmaster sent out a distress call to which the USS Farragut responded.
The Pentagon said U.S. Naval Forces Central Command is now communicating with the U.S. shipping industry on how vessels should respond to any further encounters that they perceive to be threatening, and how to report requesting assistance from the Navy.
The Navy said it will respond to any threat to U.S.-flagged ships transiting the sea lanes in the region.