The US army chief claims a US warship commander 'had literally given the order to fire' on an Iranian boat in the Strait of Hormuz.

One of the officers "had literally given the order to fire and it turns out one of the fast boats turned about simultaneously", Chairman of the US Joint Chiefs of Staff Admiral Mike Mullen said Wednesday referring to the January 6 incident involving a radio communication between Iranian guard boats and a US Navy warship.

The top uniformed US officer further said that the United States had to trust judgments of its commanders.

"From my perspective there is wisdom in relying on their judgement, as we did the other day," he told the House Armed Services Committee.

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The Pentagon last month alleged five Iranian boats belonging to the Islamic Revolution Guards Corps (IRGC) had harassed three US Navy warships by threatening to 'blow them up'.

Pentagon officials later backed off from the previous claim, saying that they do not know the source of the radio transmission.

Iran maintained that the incident was an 'ordinary' maritime identification check which ended without hostility as shown in the footage released later by the IRGC. No shots were traded during the incident.