A U.S. Navy patrol boat fired a warning shot at an Iranian military ship Tuesday as it made an alarmingly fast and close approach in the Persian Gulf.

The unidentified Iranian Revolutionary Guard Corps vessel got within 200 yards of the USS Thunderbolt before the American patrol boat fired the warning shot, quickly ending the encounter. A Pentagon official described it as an isolated incident and said one person was hurt.

It is not clear where in the Persian Gulf the incident occurred. The vessel, based in Norfolk, can carry a crew of 27 and is used primarily to patrol coastlines and provide surveillance.