"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 waterway if it was attacked.

Washington says its warships were threatened by Iranian craft in the Strait of Hormuz in January. Tehran dismissed it as a routine contact and accused the United States of exaggerating for propaganda purposes.

Asked whether he was worried incidents between U.S. naval ships and Iranian guard boats could escalate, Cosgriff said he was concerned because he did not know whether the Iranian vessels were controlled directly by the government in Tehran or by local commanders.

The Fifth Fleet is based in Bahrain.

Iran is embroiled in a standoff over its nuclear ambitions with the West, which says Tehran wants to make atomic bombs. Iran says it has only peaceful plans to produce electricity.