The incident, which ended after the Iranian boats turned away with no shots fired, occurred as President Bush prepared to visit the Middle East for talks this week. It considerably raises tensions between Iran and the United States.
The US Navy routinely encounters Iranian boats in the region, but the actions of the Iranian Navy on Sunday are "more serious than we've seen," said Vice Adm. Kevin Cosgriff, commander of the US Fifth Fleet.
"These are unnecessarily provocative [actions] in international waters," Admiral Cosgriff told reporters by videoconference from his headquarters in Bahrain.
Three US Navy ships – the cruiser USS Port Royal, the destroyer USS Hopper, and the frigate USS Ingraham – were on patrol about 12 miles from Iranian territory in the Strait of Hormuz early Sunday when five small boats associated with Iran's Revolutionary Guards approached them, Pentagon officials said. The fast boats, highly maneuverable patrol craft, were "visibly armed," a Pentagon spokesman said, and began aggressive maneuvers against the three American ships, steaming in formation into the Persian Gulf.
The boats got within 200 to 500 yards of the American ships before splitting into two groups. At least one of the fast boats then dropped several white boxes in the water in the pathway of the Ingraham, which successfully dodged them, considering them potential floating mines. Commanders of the US ships also received radio communications thought to be from one of the Iranian boats in which they heard an individual say in English, "I am coming at you. You will explode in a couple of minutes."
A Navy official said it was impossible to determine if the radio transmission actually came from one of the five boats.
Taken together, however, the American ships began to employ other evasive maneuvers and were prepared to "take appropriate action" before the five boats turned away, officials said.
One of the US ships was reported to be on the verge of shooting at one of the Iranian boats but apparently the boats turned away before the commanding officer gave that command, officials said.
Navy officials would not be specific about the kinds of precautions the US ships took, citing the classified nature of the rules of engagement during such incidents.
Cosgriff said it's dangerous for Iranian boats to provoke American ships in such a way because US naval ships are prepared to defend themselves as they ramp up their procedures in response to a threat.
"When they act that way, it raises the possibility of a miscalculation on their part and that someone might take it too far as we are stepping through our procedures," he said.
Although the US Navy has routine encounters with Iranian ships in the region, including those belonging to Iran's Revolutionary Guard, most exchanges are proper and without incident, he said.
Iran's Foreign Ministry minimized the incident on Monday, saying that it was "something normal," a characterization that Cosgriff disagreed with.
"What we're doing now is reviewing the situation and trying to make a determination to see what level we would lodge some form of formal protest or discussions with the Iranians with this thing," says a State Department official who spoke on condition of anonymity because of the sensitivity of the issue.
Also on Monday, two F-18 Hornet jetfighters based on the aircraft carrier Harry S. Truman now in the Persian Gulf, crashed into waters there. Two pilots and one crew member were recovered and are in good condition, but both planes were lost at sea, Navy officials said. The incident did not appear to be related to the confrontation between the Iranian and US navies.
The Strait of Hormuz, a narrow passageway between Iran, Oman, and the United Arab Emirates, is a strategically critical waterway through which as much as 40 percent of the world's oil exports are shipped. Last March, Iranian naval vessels captured 15 British Royal Navy sailors and Marines and held them for nearly two weeks before releasing them in what Iranian President Mahmoud Ahmadinejad said was an Easter present to the British people.
The US and its allies have long been concerned that Iran could block the passageway, crippling oil shipments out of the Gulf, according to Anthony Cordesman, a senior security expert at the Center for Strategic and International Studies.
"While the threat from Iran's conventional military may be real, the more dangerous threat is that of extremists groups' asymmetric attacks on oil facilities," he wrote in a 2006 report. "There is no attack-proof security system. It may take only one asymmetric or conventional attack on ... tankers in the Strait of Hormuz to throw the market into a spiral."