The US and Iran have engaged in their most serious military confrontation in recent times, with American warships on the verge of opening fire on gunboats of the Revolutionary Guards which had threatened to blow them up.
The incident, details of which were confirmed by the Pentagon yesterday, came on the eve of President George Bush's visit to the Middle East and follows claims by US commanders in the Persian Gulf that Iran was trying to destablise the region.
The three US ships and five Iranian vessels clashed in the early hours of Sunday in the Strait of Hormuz, the stretch of water where a 15-strong British naval party was taken hostage by the Revolutionary Guards last year. American officials at the time said that a similar attempt to seize their personnel would have led to immediate retaliation.
The Pentagon claimed the American ships were in international waters, although the demarcation of the border between Iran and Iraq on the Strait remains a matter of dispute. An American official said that the Revolutionary Guards boats "swarmed" to within 200 metres of the USS Port Royal, destroyer USS Hopper and frigate USS Ingraham and the Iranians transmitted a radio message saying: " I am coming at you; you will explode in a couple of minutes".
The captain of one of the US vessels was "literally moments away" from giving the order to open fire when the Iranian vessels moved away, American officials said. The Iranian boats were observed before the stand-off, dropping "small white containers" into the water, the Americans said, an exercise for laying mines.
"It is the most serious provocation of this sort that we've seen yet," a Pentagon spokesman said. "There were no injuries, but there could have been." The White House has warned Tehran that such "hostile action" will not be tolerated.
The US State Department spokesman, Sean McCormack, said: "The United States will confront Iranian behaviour where it seeks to do harm either to us or to our friends and allies in the region. There is wide support for that within the region."
In Tehran, a Foreign Ministry spokesman, Mohammad Ali Hossein, confirming that there had been a confrontation, added: "The example that happened at the weekend was similar to previous cases and is an ordinary and natural issue."
Tensions between Washington and Tehran over Iran's nuclear programme continue, and both the Americans and the British have repeatedly charged the Iranians with supplying explosives which have been used to kill coalition troops in Iraq.
In October, the US accused the Revolutionary Guards of trying to obtain chemical and biological weapons and its Quds force of supporting terrorism. The following month, the US military claimed that the Revolutionary Guards have taken over operations in the Gulf from the Iranian navy.
One aim of President Bush's visit to the region is expected to be to reassure Gulf states nervous about Tehran's intentions of continuing US support. American officials have noticeably ratcheted up their rhetoric about Iran. At a security conference in Manama, Bahrain, last month, Admiral William J Fallon, head of the US Central Command, said: "Their behaviour has really been a problem ... to the extent it destablises the region, which it does."
Vice-Admiral Kevin J Cosgriff added that the main concern was Iran's "threat to attempt to close the Strait of Hormuz to normal merchant marine traffic ... mines, coastal cruise missiles, tactical aviation, submarines and ships could be used to close the waterway." An American-led multinational naval force of 45 vessels, including British ships, patrols the Gulf.
More than 45 per cent of the world's oil trade flows through the Strait. After revelations about the confrontation between the Iranians and the Americans, the price of crude jumped 49 cents to $98.40 a barrel before slipping back later.
* Although only 34 miles wide at its narrowest point, the channel between Oman and Iran is of massive strategic importance, providing a crucial import and export route for world energy supplies.
More than 20 per cent of the world's total oil supply passes through the strait, with tankers carrying the liquid riches of Saudi Arabia and other Gulf states on to the Gulf of Oman and the Arabian Sea.
If the Strait of Hormuz was blocked, only a small fraction of the 17 million barrels of crude that travel along it every day would be able to pass along alternative routes. Iran has threatened to impede trade through the waterway if attacked, which would lead to a massive rise in energy prices.
Ownership of the region's waterways is disputed, particularly near the southern borders of Iraq and Iran, and hostile military action is not unheard of: last March, Iran seized Royal Navy personnel accused of trespass in Iranian waters. The channel is also used to transport heavy armour and military supplies to Iraq and other Gulf states.Reuse content