The five Iranian boats approached the warships Sunday as they passed through the Strait of Hormuz on their way into the Persian Gulf. U.S. officials said the Iranians dropped objects in the water around the American ships and threatened to blow them up.
Naval officers were on the verge of firing when the smaller vessels broke off and retreated, they said.
The encounter drew high-level attention from the Bush administration, and U.S. officials demanded an explanation and warned Iran to avoid another confrontation. Iranian officials said the encounter was normal and ended as soon as the vessels were identified.
The confrontation is likely to reawaken a debate over Iran's intentions concerning the U.S. presence in and around Iraq.
Some U.S. officials have concluded that Tehran has been using its influence recently to reduce attacks on U.S. forces in the region. Others, however, contend the evidence is not clear.
Defense Secretary Robert M. Gates said the incident was a reminder of the unpredictability of the Iranian government and said he hoped that Tehran would disavow the action of the boats.
"I found the action by the Iranians quite troubling, actually, and a matter of real concern," Gates said shortly after touring the amphibious assault ship New Orleans in San Diego and examining its defenses against small boats. "This is a very volatile area. And the risk of an incident, and an incident escalating, is real."
Senior Pentagon officials said they were puzzled about the purpose of the confrontation. A military official said officers were still trying to determine whether the Iranians were attempting to attack and were thwarted, or if the confrontation was designed to test American defenses.
"Is this indicative of future kinds of harassment?" asked the military official, speaking on condition of anonymity because he was discussing the internal thinking. "We do not know their intent."
The Iranian boats were under the control of the Revolutionary Guard, an elite military force allied with Iranian hard-liners. Before the encounter, the U.S. flotilla had passed regular Iranian navy forces operating in the Gulf of Oman without incident. U.S. officials expressed concern in November at indications that the Revolutionary Guard had taken command of all Iranian navy vessels in the gulf.
An official in the Revolutionary Guard who was quoted by the semiofficial Fars News Agency downplayed the incident as a routine encounter in the cramped waterways of the gulf.
"Three U.S. boats were about to enter Iranian waters and they were questioned normally," the official said, according to the report, which did not disclose his name.
"Nothing important happened between the Revolutionary Guards and the American boats in international waters. The Americans were identified and everything went well."
News of the incident surfaced as President Bush prepared to leave today for an eight-day trip to the Middle East, aimed in part at marshaling support from gulf states for administration proposals to pressure Iran.
Sean McCormack, the chief State Department spokesman, said he did not believe the incident was intended to send a signal before Bush's trip.
The incident began about 5 a.m. Sunday as the cruiser Port Royal, destroyer Hopper and frigate Ingraham sailed toward the Persian Gulf. Vice Adm. Kevin J. Cosgriff, the commander of the U.S. 5th Fleet, said five Iranian boats maneuvering aggressively sped toward the three warships.
The Iranian boats split into two groups and approached the U.S. ships from both sides, Cosgriff said, speaking to reporters via a teleconference from Bahrain. Officials said the boats came within 200 yards of the warships and radioed the Americans."They said something like, 'I am coming at you and you will explode,' " a military official said. "That is overt aggression."
Cosgriff said that after the radio exchange, two of the boats dropped white boxes into the water, in the path of the Ingraham. The boxes floated but did not explode. After about 30 minutes, Cosgriff said, the Iranians retreated northward, toward their territorial waters.
"The behavior of the Iranian ships was, in my estimation, unnecessary," Cosgriff said, calling the maneuvers "unduly provocative."
The Navy boosted its defense against small-boat attacks after the 2000 assault on the destroyer Cole in Yemen by suicide bombers using such a craft. Navy commanders also reviewed their procedures for dealing with the Iranian navy after a British vessel was captured by Iran last year and 15 crew members were held for 13 days.
U.S. military officials were anxious not to escalate the incident, but the confrontation brought to life the worst fears of U.S. commanders in the region.
Officials have said recently that they fear military conflict with Iran could be touched off by a small-scale conflict, perhaps related to Iraq, in the waters of the Persian Gulf or in the border regions.
In Tehran, the incident prompted fears that hard-liners are trying to sabotage efforts to reduce tensions between Washington and Iran.
One source close to Iran's hard-line camp said Iranians follow strict guidelines to prevent U.S. or other forces from straying into their territorial waters.
"It is general rule, so if U.S. forces trespass, we will respond," said the source, who spoke on condition of anonymity.
Times staff writers Borzou Daragahi in Beirut, Peter Spiegel in San Diego and Paul Richter in Washington, and special correspondent Ramin Mostaghim in Tehran contributed to this report.