Tensions rise as US navy claims clash with Iran vessels · Pentagon says its warships were harassed on oil route · Incident coincides with nuclear chief's Tehran trip Dan Glaister in Los Angeles Tuesday January 8, 2008 The Guardian Tensions between the US and Iran resurfaced yesterday when Pentagon officials alleged that Iranian warships had threatened three US navy vessels in the Strait of Hormuz. The incident comes after a period of relative calm in relations between the two countries, and ahead of a rare visit to Iran by the head of the International Atomic Energy Agency, Mohamed ElBaradei. According to Pentagon officials, US forces had been on the point of firing on the revolutionary guard boats when the Iranians turned away. A White House spokesman, Tony Fratto, said: "We urge the Iranians to refrain from such provocative actions that could lead to a dangerous incident in the future." In Tehran, the foreign ministry suggested that its boats had not recognised the US vessels. A spokesman, Muhammad Ali Hosseini, played down the incident, saying that it was "similar to past ones ... That is something normal that takes place every now and then for each party, and it [the problem] is settled after identification of the two parties," he told the state news agency IRNA. Pentagon officials said the incident occurred early on Sunday as a US frigate, destroyer and cruiser passed through the strait, a strategic oil route. Five small boats, thought to be from the Revolutionary Guard, passed in front of the US vessels, dropping boxes in the water to force them to take evasive action. Describing the confrontation as "significant", a Pentagon official said the Iranians had radioed the US ships with a message to the effect that "we're coming at you and you'll explode in a couple of minutes". The Iranians moved away "literally at the very moment that US forces were preparing to open fire ... It is the most serious provocation of this sort that we've seen yet," the official added. A US defence department spokesman claimed the Iranians were operating at "distances and speeds that showed ... reckless, dangerous and potentially hostile intent. At least some were visibly armed. Small Iranian fast boats made some aggressive manoeuvres against our vessels and indicated some hostile intent." The allegation echoes an incident in March last year when revolutionary guards held 15 British sailors for nearly two weeks after alleging that they had strayed into Iranian waters. A US state department spokesman said it would not lodge a formal protest, but added: "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." Relations between the US and Iran have been fraught in recent years, with Washington voicing concern over Iran's alleged nuclear programme and the alleged role of the revolutionary guards in fomenting unrest in neighbouring Iraq. Iran is under two sets of UN sanctions for its refusal to freeze uranium enrichment. However, a recent US intelligence assessment concluded that Iran had shut down its clandestine nuclear weapons programme in 2003. In May last year the US ambassador to Iraq, Ryan Crocker, met his Iranian counterpart, breaking a 27-year diplomatic freeze between the countries. This week, ElBaradei will go to Tehran at the invitation of the Iranian government. His office said the trip was intended to enable the IAEA to develop ways to "enhance and accelerate" nuclear safeguards in Iran. But western diplomats said ElBaradei might tell Tehran that the intelligence estimate does not free it of obligations to the IAEA. "He may want to tell Iran, 'This is your last chance, don't make me look an idiot,' to light a fire under their feet," a western diplomat told Reuters. The Hormuz incident comes as George Bush tomorrow prepares to make the first major trip of his presidency to the Middle East. He is expected to meet leaders of Egypt, Saudi Arabia and other nations, and weigh in on the faltering Palestinian-Israeli peace process as well as seeking support for US concerns about Iran.