Doubts grow over Iranian boat threats · Pentagon climbdown over 'you will explode' video · Mystery remains over where voice came from Ed Pilkington New York Friday January 11, 2008 The Guardian Doubts intensified last night over the nature of an alleged aggressive confrontation by Iranian patrol boats and American warships in the Persian Gulf on Sunday, after Pentagon officials admitted that they could not confirm that a threat to blow up the US ships had been made directly by the Iranian crews involved in the incident. Several news sources reported that senior navy officials had conceded that the voice threatening to blow up the US warships in a matter of minutes could have come from another ship in the region, or even from shore. The concession came on the day that a formal American complaint was lodged with Iran over the incident, and just 24 hours after President George Bush, on tour in the Middle East where he will be discussing policy towards Iran, warned Tehran to desist from such aggression and said any repetition would lead to "serious consequences". The Pentagon alleges that the confrontation lasted about 20 minutes and took place in the Strait of Hormuz, where the US ships were in international waters. Five Iranian patrol boats swarmed around three US warships and came within a threatening 200 metres, prompting US personnel to be put on alert. The US navy has said that its gunners came within seconds of firing on the speedboats. On Tuesday, the US administration released video footage that it said showed the Iranian speedboats harassing the American vessels. A voice in English with a strong accent was heard to say: "I am coming at you - you will explode in a couple of minutes." Yesterday the Iranians put out their own four-minute video that showed an Iranian patrol officer in a small boat communicating with one of the US ships. "Coalition warship number 73, this is an Iranian navy patrol boat," the Iranian said. An American naval officer replied: "This is coalition warship number 73 operating in international waters." The voice of the Iranian sailor in Tehran's footage was different to the deeper and more menacing voice, threatening to blow up the warships in the US version. Nor was there any sign of aggressive behaviour by the Iranian patrol boats. The Strait of Hormuz is a particularly sensitive stretch of water, both economically as a key shipping route for oil from the Gulf, and militarily. The location, together with memories of the arrest of 15 British sailors by the Iranians last year and their detention for two weeks, is likely to have heightened nerves on both sides. But the mystery remains of where the voice that apparently threatened to bomb the US ships came from. The Pentagon has said that it recorded the film and the sound separately, and then stitched them together - a dubious piece of editing even before it became known that the source of the voice could not, with certainty, be linked to the Iranian patrol boats. A post on the New York Times news blog yesterday from a former naval officer with experience of these waters said that the radio frequency used in the Strait of Hormuz was regularly polluted with interfering chatter, somewhat like CB radio. "My first thought was that the 'explode' comment might not have come from one of the Iranian craft, but some loser monitoring the events at a shore facility." Despite growing doubts about what happened, the Bush administration continued to stand by claims of Iranian hostility. The defence secretary, Robert Gates, said the concern came from the "fact that there were five of these boats and that they came as close as they did to our ships and behaved in a pretty aggressive manner". Further attention will focus on Tehran from today when Mohamed ElBaradei, head of the International Atomic Energy Agency, begins a two-day visit for talks on Iran's nuclear programme.