The U.S. vowed Monday to "confront Iranian behavior" after five Revolutionary Guard boats allegedly surrounded three U.S. Navy ships in the Strait of Hormuz and threatened to blow them up.
A Pentagon official said the five Iranian speedboats "pretty much swarmed" the three U.S. vessels in international waters about 4 a.m. GMT on Sunday, with the Iranians threatening that one of the U.S. ships would blow up in minutes.
"I am coming at you. You will explode in a couple of minutes," the radio transmission from one of the Iranian ships said, according to the officials.
The captain of one of the U.S. ships in the strait, a major oil shipping route off the Iranian coast, was in the process of giving an order to fire but the Iranian boats moved away, an official said.
The officials said it was not unusual for Iranian boats to get close to U.S. ships in the strait but the radio transmission was unusual. They said the Iranian vessels also dropped small white boxes into the water. It was not clear what the boxes contained.
One official said the move may have been an attempt to ascertain what tactics the U.S. ships would use if objects were dropped into the strait.
The incident occurred on the eve of a visit to the Middle East by U.S. President George W. Bush, who said last week that one of the aims of his trip was to counter Iran's ambitions in the region.
The White House meanwhile promised swift retaliation.
"The United States will confront Iranian behavior where it seeks to do harm either to us or our friends or allies in the region. There is wide support for that within the region," State Department spokesman Sean McCormack told reporters.
Washington has been engaged in a long standoff with Tehran over Iran's nuclear program.
In October, the United States designated the Revolutionary Guard Corps a proliferator of weapons of mass destruction and its elite Quds force a supporter of terrorism.
In March, Iran seized 15 British sailors and marines in the Gulf and accused them of trespassing in Iranian territory while they inspected a merchant vessel. London maintained the British personnel were in Iraqi waters.
The British personnel were held for almost two weeks before being freed in what Iranian President Mahmoud Ahmadinejad said was a "gift" to the British people.
In Tehran, an Iranian foreign ministry spokesman had no immediate comment on U.S. accounts of the incident in the Strait of Hormuz.