U.S. officials say Iranian patrol ships fired warning shots over a Singapore-flagged cargo vessel in the Persian Gulf on May 14.
It was the second Iranian confrontation with an unarmed commercial ship in the last month.
The officials said boats manned by Iran's Islamic Revolutionary Guards Corps fired across the bow of the Alpine Eternity in international waters off the coast of the United Arab Emirates (UAE).
The officials said the commercial ship then headed toward the UAE and the Iranian boats fired a second wave of warning shots.
The Iranian ships departed the area when the UAE deployed coast guard boats.
The Alpine Eternity is involved in a financial dispute with Tehran, the officials said. The ship on March 22 accidentally struck an Iranian oil platform, damaging it.
The ship also was damaged in the accident and went into port for repairs. During that period, the Iranians informed the shipping company that it must pay for damage to the oil platform, but the ship left port without settling Iran's claim.