Last Updated Apr 28, 2015 6:30 PM EDT
A Marshall Islands-flagged cargo ship - the Maersk Tigris - has been boarded by Iranians and is being escorted to Bandar Abbas. No Americans on board, reports CBS News correspondent David Martin.
The Tigris was transiting the Strait of Hormuz when it went inside Iranian territorial waters. Iranians ordered it to halt. The captain refused, so Iranians fired shots across the bow.
The captain then sent out a distress call, so the U.S. Navy sent a destroyer and aircraft, which began monitoring the situation. However, Pentagon lawyers have determined that U.S. has no obligation to come to the defense of a Marshall Islands-flagged vessel at sea, reports Martin.
Saudi-owned Al Arabiya television had reported that an Iranian "force" seized a U.S. cargo ship after opening fire on it in the Gulf on Tuesday and directed it to the Iranian port of Bandar Abbas, but Pentagon officials tell CBS News this is not the case.
Commercial ships are often manned by crews from nations other than the one where the vessels are registered - meaning that, even if it had been a U.S.-flagged ship, the crew could easily have been from elsewhere.
On April 24 Iranian small boats harassed a U.S.-flag cargo ship, the Maersk Kensington, as it was transiting the Strait of Hormuz. For 15 minutes four Iranian Revolutionary Guard Corps patrol boats buzzed around the ship, pointing their guns at it.
Martin reports that Tuesday's boarding of the Maersk Tigris is part of a pattern and the assumption is that it is in retaliation for having lost face last week when the Iranian convoy to Yemen turned around and headed home.
The Strait of Hormuz is vital to the international oil trade, and Iran has wielded its geographic location along the waterway's northern border as a bargaining chip in recent years, even threatening to close it to all international shipping traffic in 2012.
Earlier this year, Iran's military conducted drills near the Strait in the Persian Gulf in a show of force just off its borders.