A US Navy patrol ship fired warning shots at an Iranian Revolutionary Guard Corps vessel in the Persian Gulf today after it approached within 150 yards. A US defence official said, the Iranian boat was coming in at a high rate of speed, it did not respond to any signals or any bridge-to-bridge calls. <br/><br/>It felt there was no choice except to fire the warning shots. The incident occurred in the northern Persian Gulf, when the Iranian vessel began to approach the USS Thunderbolt. <br/><br/>After the US ship fired the warning shots, the Iranian vessel stopped, the official said, at which point the Thunderbolt continued on its way.<br/><br/>