Four Iranian military vessels sped close to a US Navy guided missile destroyer with their weapons uncovered in the Strait of Hormuz in an "unsafe and unprofessional" encounter, a US defense official said Wednesday.

The USS Nitze shot warning flares, sounded its whistles and attempted unsuccessfully to communicate with the Iranian boats during Tuesday's incident, the official told AFP on condition of anonymity.

The encounter occurred in international waters in the strait, a vitally important choke point with Iran to its north and the United Arab Emirates to the south.

According to the Stars and Stripes military newspaper, the Nitze had to change course to avoid a possible collision, even though it was near offshore oil rigs.

The Iranian vessels came to within 300 yards (meters) of the Nitze before eventually leaving the scene, Stripes reported.

In January, the Iranian navy briefly captured the crews of two US patrol boats that had, through a series of blunders, strayed into Iranian territorial waters.

The 10 American sailors were released within 24 hours.