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 ... warned Tehran to desist from such aggression and said any repetition would lead to serious consequences". 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 [from] 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 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.