Iranian naval vessels fired warning shots at a Singapore-flagged cargo ship in the Persian Gulf Thursday, CNN reported. U.S. officials are investigating the incident.

Five purported Iranian Revolutionary Guard Corps navy boats supposedly confronted the vessel in international waters, firing shots across its bow. The Singapore cargo ship entered the United Arab Emirates' territorial waters to escape the Iranian navy. It was subsequently escorted by UAE vessels. It's unclear whether the cargo ship suffered any damage.

No American citizens or vessels were involved in the confrontation, CNN said. The operators of the Singapore ship did not contact the U.S. Navy.