The United States issued a stern warning to Iran Monday following an incident near the Strait of Hormuz in which Iranian speedboats veered dangerously close to three U.S. Navy ships and intercepted radio signals said U.S. "ships would explode."
U.S. ships blew whistles, issued radio warnings and took evasive maneuvers to avoid striking the Iranian boats, which motored as close as 200 yards from the American ships by one account. The naval ships armed their weapons, and the five unmarked Iranian boats — believed to belong to the Iran Revolutionary Guard — sped away.
The incident lasted less than 30 minutes, Vice Adm. Kevin J. Cosgriff, commander of the the 5th fleet, told reporters Monday.
"At one point during this encounter ... the ships received a radio call that was threatening in nature to the effect that they were closing our ships and that ... the U.S. ships would explode," Cosgriff said, speaking via video camera from Bahrain.
Cosgriff also called the incident "more serious than we have seen" among other encounters with Revolutionary Guard boats.
The incident also spurred a flurry of response and counter-response between the two nations.
"We urge the Iranians to refrain from such provocative actions that could lead to a dangerous incident in the future," National Security Council spokesman Gordon Johndroe said Monday.
Iran's Foreign Ministry on Monday characterized the incident as "something normal," saying it has been resolved.
Shortly afterward, Pentagon press secretary Geoff Morrell said, "This aggressive and hostile behavior by IRG (Iranian Revolutionary Guard) is a cause for real concern.
"It is perplexing why five small Iranian boats would confront three U.S. warships operating in international waters. Such actions are dangerous and could have quickly escalated.
"We see it as further evidence that Iran is unpredictable and remains a threat."
U.S. officials said a cruiser, a frigate and a destroyer were on a routine transit mission when the Iranian boats approached.
The U.S. ships were forced to take defensive action to avoid striking the close-by Iranian boats and armed their weapons, but neither side fired any shots.
The small Iranian boats also threw boxes into the water ahead of the U.S. boats before speeding off. It could not immediately be determined what was in the boxes.
The boats were not marked, and not believed to belong to the Iranian State Navy but rather the Iranian Revolutionary Guard, which Navy officials believe are more threatening and unpredictable than Iran's regular navy. Officials said Monday the boats' actions over the weekend were consistent with Revolutionary Guard, and the U.S. Navy appears resolute in its belief that the boats belonged to the group.
Pentagon spokesman Bryan Whitman described the situation as a "serious incident that deserves an explanation. ... It was careless, reckless and potentially hostile activity."
Whitman said the State Department will be involved in addressing the incident with the Iranians.
State Department spokesman Sean McCormack, however, said he was not aware of any plans to lodge a formal protest.
"Without specific reference to this incident in the Strait of Hormuz, the United States will confront Iranian behavior where it seeks to do harm either to us or to our friends and allies in the region," McCormack said. "There is wide support for that within the region and certainly that's not going to change."
Whitman said the incident began with hostile radio communications on the part of the Iranians. This caused the Navy ships to take aggressive maneuvers and to issue warnings of their own.
Whitman did not provide specifics on the radio communications or the American response, but it was clear the U.S. ships switched to a more aggressive posture upon receiving those communications from the Iranians and were "prepared to take appropriate action."
Whitman also said these Iranian boats were visibly armed. He could not say specifically what types of weapons they displayed, but said typically these boats are equipped with machine gun-type mounts.
The incident lasted 15-20 minutes. Whitman also said this isn't the first time in which Iranian speedboats have met U.S. vessels, but it has not happened recently.
The Associated Press, citing an anonymous Pentagon official, said the incident occurred at about 5 a.m. local time Sunday.
"There were no injuries but there very well could have been," the AP source said, adding that the Iranian boats turned away "literally at the very moment that U.S. forced were preparing to open fire" in self defense.
The AP source said he didn't have the precise transcript of communications that passed between the two forces, but the Iranians radioed something to the effect that "we're coming at you and you'll explode in a couple minutes."
Last March, Revolutionary Guard boats intercepted a British vessel, holding naval servicemen aboard the vessel for 15 days before releasing them.
The Strait of Hormuz is located between Oman and Iran and connects the Persian Gulf with the Gulf of Oman and the Arabian Sea. Up to 17 million barrels of oil are shipped through Strait of Hormuz each day.
And roughly two-fifths of all seaborne traded oil goes through the Strait of Hormuz. The majority of oil exported from the Strait of Hormuz travels to Asia, the United States and Western Europe.
This weekend's incident comes as President Bush's first major trip to the Middle East is approaching. While scheduled to meet the leaders of Israel, Egypt, Saudi Arabia and other regional nations Jan. 9-16, Bush is expected to try to bolster the troubled peace process between Israel and the Palestinians but is also likely to seek backing for U.S. concerns about Iran.
Iran is under two sets of U.N. Security Council sanctions for its refusal to freeze uranium enrichment, a potential pathway to nuclear arms, and Washington is pushing for additional U.N. penalties. But a recent U.S. intelligence assessment that it probably shut down a clandestine weapons program three years ago have led to increased resistance to such a move from permanent Security Council members Russia and China, which have strategic and trade ties with Tehran.
At about this time last year, Bush announced he was sending a second aircraft carrier to the Gulf region in a show of force against Iran.
The U.S. Navy quietly scaled back to one carrier group several months later. The lead carrier is the USS Truman, and is supported by several smaller boats. But while the two carriers were there, they staged two major exercises off Iran's coast.
The war games amounted to U.S. muscle-flexing at a time when Tehran increasingly was at loggerheads with the international community over its disputed nuclear program and threatened to close the strategic Strait of Hormuz for oil transports in case of a U.S. military strike on Iran.
Since then, there have been diplomatic overtures aimed at calming tensions. A May 28 meeting concerning security in Iraq between U.S. Ambassador Ryan Crocker and his Iranian counterpart, Hassan Kazemi Qomi, broke a 27-year diplomatic freeze between the two countries.
A planned Dec. 18 meeting between Iranian and American security, military and diplomatic experts was canceled a few days before it was to be held. At the time, Iranian officials said it was a scheduling problem while U.S. officials referred questions to the Iraqi Foreign Ministry.
And in the past month or so, U.S. officials have said Tehran appears to have slowed or halted the flow of illegal weapons across the frontier between Iran and Iraq. Iran has denied the arms smuggling accusations, insisting that it is doing its best to help stabilize its embattled western neighbor.
Iranians recently were reported to be upset that although they contributed to the improving security situation in Iraq, U.S. officials have not done enough to acknowledge it.
The United States maintains nearly 40,000 troops in Gulf countries other than Iraq, with the largest group in Kuwait and others in Qatar, Bahrain, the United Arab Emirates, Oman and Saudi Arabia.
FOX News' Justin Fishel and The Associated Press contributed to this report.