The Iranian boat is believed to have been operated by the Iranian Revolutionary Guard Corps, according to a defense official familiar with details of the incident. The officials said the Iranian boat approached and came within 150 yards of the US ship.

The Iranians did not respond to any warnings from the US ship, including radio calls, firing of flares and five short blasts from the US Navy ship’s whistle, which is the internationally recognized communications signal for danger, the officials said.