A fleet of high-speed Iranian boats, which threatened a U.S. naval convoy passing near Iranian waters, fled the scene as the American commanders were preparing to open fire.
According to The Associated Press, the confrontation ended without incident.
The U.S. fleet consisted of three warships -- cruiser USS Port Royal, destroyer USS Hopper and frigate USS Ingraham, which were sailing into the Persian Gulf through the Straits of Hormuz.
The U.S. Navy said the ships were in a routine passage in international waters when five small boats, presumed to be part of Iran's Revolutionary Guard Corps Navy, approached them at high speed, coming within three-tenths of a mile and maneuvering "aggressively."
Vice Adm. Kevin Cosgriff, commander of the U.S. 5th Fleet, said the ship commanders were preparing to open fire when the Iranian fleet fled back toward its shore.
Cosgriff said the U.S. fleet received threatening radio messages "to the effect that they were closing our ships and the U.S. ships would explode."
"Subsequently, two of these boats were observed dropping objects in the water, generally in the path of the final ship in the formation, the USS Ingraham," said the admiral.
"These objects were white, box-like objects that floated. Obviously, the ship passed by them safely," he said. The boxes were not retrieved so it's not known if they actually posed a threat.
"We take this deadly seriously," Cosgriff said in a radio-linked report to the Pentagon from Bahrain, citing the October 2000 terror attack on the USS Cole in Yemen's Aden harbor, which killed 17 U.S. sailors and nearly sunk the ship.
"We are going to confront Iran's behavior where it threatens us, where it threatens our allies, where it threatens the integrity of the international systems that have been set up to facilitate international commerce and finance," U.S. State Department spokesman Sean McCormack told the press.