The Pentagon released dramatic footage last night showing how American warships were seconds away from opening fire on Iranian gunboats that swarmed around a US Navy squadron as it entered the crowded Strait of Hormuz on Sunday.

As the Iranian patrol boats closed in, a voice threatened over the radio: “I am coming to you. You will explode after two minutes.”

The four-minute video, of an incident that lasted 20 minutes, was shot from the bridge of the USS Hopper, a destroyer that was leading the cruiser USS Port Royal and the frigate USS Ingraham into the Gulf through international waters.

The Pentagon pictures suggested that the incident, dismissed by Iran as an “ordinary occurrence”, very nearly triggered a clash in one of the world’s busiest sea lanes, through which a quarter of the world’s crude oil passes.

President Bush, who set off last night on an eight-day visit to the Middle East, described the incident as a “dangerous situation”.

“They should not have done it, pure and simple,” Mr Bush said. “I don’t know what their thinking was, but I’m telling you what I think it was — I think it was a provocative act.”

In the video the Iranian speedboats, thought to belong to the elite Islamic Revolutionary Guards Corps, can be seen racing across the grey waters of the Gulf ignoring horn blasts and radio warnings from the much-larger and better-armed American vessels.

One bright-blue Iranian boat, manned by a crew in orange jump suits, can be seen snaking through the wake of the American warships, apparently dropping boxes into the water.

An unidentified US sailor on the bridge of the USS Hopper can be heard trying to contact the Iranians by radio: “This is coalition warship. I am engaged in transit passage in accordance with international law. Intend no harm.” He then asks the Iranians to “identify yourself and state your intentions”.

But with the Iranian vessels still closing in, the American crewman warns the Iranians that they could come under fire. “Inbound small craft, you are approaching a coalition warship operating in international waters. Your identity is unknown, your intentions are unclear,” he says. He then warns them that they would be “subject to defensive measures” if they did not disengage.

“Request that you alter course immediately to remain clear,” the American crewman says. After a pause, a man with a heavy accent replies in English: “You will explode after two minutes.”

The American asks him to repeat the message, but the Iranian vessels, which at one point came within 200 yards of the American ships, then disengage and return to base.

Tehran has tried to play down the incident. “This happens for the two sides every once in a while and, after the identification of the two sides, the issue is resolved,” a Foreign Ministry spokesman in Tehran said.

There are suspicions that the action was linked to Mr Bush’s visit to the region, where he is expected to rally support against the regime in Iran and its militant Palestinian and Lebanese allies. Mr Bush’s tour through Kuwait, Bahrain, Abu Dhabi, Dubai and Saudi Arabia will be seen as a provocation in Tehran.

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