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Washington stepped up its war of words against Iran last night as the US military released video and audio recordings of the confrontation between a three-ship Navy convoy and five small Iranian boats in the Persian Gulf.

As President George Bush prepared for a nine-day, six-country tour of the Middle East, the US Navy released just over four minutes of recordings from the two countries' most serious military confrontation in recent times. Mr Bush described the stand-off, in the Strait of Hormuz, as "a provocative act" by the Iranians.

The jerky footage, shot from one of the US ships, shows several small Iranian boats approaching at high speed as a voice apparently threatens: " I am coming at you. You will explode." This is followed by an American voice saying: "Inbound small craft: You are approaching a coalition warship operating in international waters. Your identity is not known; your intentions are unclear. You are sailing into danger and may be subject to defensive measures."

The recording begins with a crew member speaking into a ship-to-ship radio after the Iranian boats are spotted. He says: "This is coalition warship. I am engaged in transit passage in accordance with international law ... This is coalition warship. I am engaged in transit passage in accordance with international law. I intend no harm. Over."

The tense scene – which the US says lasted 20 minutes – occurred on the same stretch of water where a 15-strong group of British naval officers were taken hostage by the Iranian Military Guard last year. Iran dismissed the latest incident as a "routine" encounter.

The Pentagon has described the incident as "the most serious provocation of this sort we've seen yet."

It comes after apparently receding prospects of a military strike after last year's intelligence assessment that Iran had shelved active pursuit of a nuclear weapons programme in 2003.

Mr Bush, speaking in the White House Rose Garden hours before flying to Israel – which questions the intelligence assessment of Iran's aborted nuclear programmes – said: "I don't know what [the Iranians'] thinking was, but I'm telling you what I think it was: I think it was a provocative act."

In the footage, a blue speedboat with at least two crew is visible as a navy crewman can be heard over the radio, saying: "Request you establish communications, identify yourself and state your intentions, over."

The officer refers to "five unidentified small surface" boats, as the ships' sirens wail in the background. At the end of the US recording, the screen goes black and the remainder is in partly unclear audio.

* Mr Bush arrives in Israel amid a massive security presence involving more than 10,000 police and uncertainty over whether his visit will give much-needed impetus to the nascent Israeli-Palestinian negotiating process. On the eve of the three-day visit to Israel and the West Bank, the first since he took office seven years ago, the Israeli Prime Minister Ehud Olmert and the Palestinian President Mahmoud Abbas have agreed a framework for talks which would cover all the main topics relating to a future Palestinian state. There are no plans for a joint meeting between the three leaders.