American naval forces have started "accompanying" American-flagged commercial ships passing through the Strait of Hormuz, defense officials said Thursday, according to the AFP news agency.
The move comes after Iran seized a Marshall Islands-flagged vessel this week.
It means American warships will be in the area and in contact with commercial vessels but not carrying out a full-fledged escort, officials in Washington said.
"U.S. naval forces have begun accompanying U.S.-flagged maritime traffic in the Strait of Hormuz," a defense official quoted by AFP said.
The security precaution did not require the deployment of more US ships in the area and naval commanders "will coordinate with shipping industry representatives to ensure accompanying operations are conducted smoothly and efficiently," the official added.
The warships "are close enough to respond if needed" and "in communication" with the cargo ships, but not necessarily within eye sight, a defense official said.
The measure signaled Washington's determination to safeguard commercial shipping in the strategic waterway and to counter any potential attempt by Iran to disrupt American-flagged vessels heading through the narrow shipping channel.
About 30 percent of all oil traded by sea moves through the chokepoint, or about 17 million barrels a day.
Iranian patrol boats forced a Marshall Islands-flagged ship, the Maersk Tigris, to Iran's Larak Island on Tuesday after firing warning shots. And last week, Iranian forces "harassed" a U.S.-flagged commercial ship in the Gulf.
The incidents prompted Washington to demand Iran uphold freedom of navigation and the provisions of the law of the sea.
Iran has said it seized control of the container ship due to a commercial dispute with Denmark's giant Maersk group, which chartered the vessel to ferry cargo in the region.
When it was intercepted, the Tigris was traveling on an international shipping route within Iran's territorial waters.
Iran’s Foreign Minister, Mohammad Javad Zarif, said after the incident that his country remains “committed to freedom of movement on the high seas.”
He did not, however, directly comment on the Iranian seizure of the Maersk Tigris.