Abu Dhabi - The United States will not allow Iran to block the Gulf, which carries crude from the world's largest oil exporting region, and would defend its ships in the waterway, the U.S. Navy's Fifth Fleet said on Wednesday.

    "I believe ... Iran will not attempt to close the Strait of Hormuz and we will not allow them to close the Strait of Hormuz. I can't say it anymore clearly than that," Vice-Admiral Kevin Cosgriff, the commander of the U.S. Navy's Fifth Fleet, told a conference on Gulf naval security in Abu Dhabi.

    The head of Iran's Revolutionary Guards said in remarks published last week that Tehran would impose controls on shipping in the Gulf and the strategic Strait of Hormuz if it was attacked.

    Fear of an escalation in the standoff between the West and Iran, the world's fourth largest oil producer, has helped propel oil prices over $140 a barrel.

    Speculation about a possible attack on Iran because of its nuclear program has risen since a report last month said Israel had practiced such a strike.

    Western powers say they fear Iran is seeking to develop nuclear weapons under cover of a civilian nuclear program. Tehran says the work aims to generate power.

    "Regardless of what might precipitate an entity or a country to attempt to close the strait ... it is an international affront that is saying to the world that the nearly 40 percent of the world's oil and the significant amount of natural gas which goes through the strait is now being held hostage by a single country," he said.

    "I think the international community would find its voice rapidly and insist that whoever was attempting to do this cease and desist."

    There have been repeated incidents in the Gulf, where the Fifth Fleet is based, in which the U.S. ships have come close to skirmishing with approaching boats in the busy waterway.

    A cargo ship hired by the U.S. military fired warning shots at approaching boats in the Gulf in April, underscoring regional tensions. In January, the United States said five small Iranian speedboats aggressively approached three U.S. Navy ships in the start and warned they could explode.

    Iran said its boats were simply trying to identify the U.S. vessels and military experts have since said the warning may have come from an independent radio operator.

    Asked whether he was worried such incidents could escalate, Cosgriff said U.S. naval officers would defend their ships.

    "There is not a captain or admiral in the United States Navy who does not know we buried 20 sailors to successful small boat attacks against our ships...over the last eight years," he said.

    "There is not a captain or admiral in the United States Navy who is not ready to defend his or her ship to their utmost capability."

    Part of the problem, he said was that it was not clear who was in control of the Iran's Revolutionary Guard naval activities -- Tehran or local commanders.

    "I am concerned about that country's ability to control its own armed forces and in this case the Revolutionary Guard forces and I think the region should be concerned about that," he added.

    -------

    Writing by Ola Galal; Editing by Dominic Evan