|PIC1|Five Iranian boats made aggressive manoeuvres and showed hostile intent towards three U.S. Navy ships at the weekend in the Strait of Hormuz, a major oil shipping route in the Gulf, the Pentagon said on Monday.

The Pentagon said the incident was serious. It described the Iranian actions as "careless, reckless and potentially hostile" and said Tehran should provide an explanation.

In Tehran, the Iranian foreign ministry described the incident as ordinary.

"The example that happened on Saturday was similar to previous cases and is an ordinary and natural issue," Foreign Ministry spokesman Mohammad Ali Hosseini told Iran's official IRNA news agency.

"This is an ordinary issue that happens for the two sides every once in a while and, after the identification of the two sides, the issue is resolved."

The incident was the latest sign of tension between Washington and Tehran, at odds over a range of issues from Iran's nuclear programme to U.S. allegations of Iranian support for terrorism.

U.S. President George W. Bush is due to travel to the Middle East this week on a trip he has said is partly aimed at countering Iranian influence.

"We urge the Iranians to refrain from such provocative actions that could lead to a dangerous incident in the future," White House spokesman Gordon Johndroe said.

Oil prices briefly rose on the news about the confrontation as dealers weighed the threat to oil shipments along the key shipping route. Crude futures jumped 49 cents to $98.40 a barrel before slipping back.

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.

Pentagon spokesman Bryan Whitman said the three U.S. ships had been in international waters passing through the Strait of Hormuz on Sunday when they were approached by five fast boats, at least some of which were visibly armed.

"This is a serious incident," Whitman said. "Clearly this is something that deserves an explanation."

"AGGRESSIVE MANOEUVRES"

The boats were identified as Iranian and "made some aggressive manoeuvres against our vessels and indicated some hostile intent", Whitman said.

"This required our vessels to issue warnings and conduct some evasive manoeuvring," Whitman told reporters. "The U.S. Navy vessels were prepared to take appropriate actions... but there was no engagement of the vessels."

Other Pentagon officials, speaking on condition of anonymity, said the Iranians made threats by radio and a U.S. captain was in the process of ordering sailors to open fire when the Iranian boats moved away.

The incident took place about 4 a.m. British time on Sunday, or late Saturday night in Washington, the officials said.

According to the officials, the radio transmission from one of the Iranian ships said: "I am coming at you. You will explode in a couple of minutes."

The Iranian boats were believed to belong to Iran's Revolutionary Guard, the officials said.

In October, the United States designated the Revolutionary Guard Corps a proliferator of weapons of mass destruction and its elite Qods force a supporter of terrorism.

An "informed source" from the naval force of the Revolutionary Guards was quoted by Iranian state television as saying: "There were no out of the ordinary contacts between the Guards' naval force and American ships."

In his account of the incident, the source said three U.S. naval ships were asked by Guards' vessels "as usual" to identify themselves "which they did and they continued their path".