A US Navy patrol ship fired warning shots at an Iranian Revolutionary Guard vessel Tuesday after it approached within 150 yards (137 meters), a US defense official said. 

"The IRGCN boat was coming in at a high rate of speed. It did not respond to any signals, they did not respond to any bridge-to-bridge calls, they felt there was no choice except to fire the warning shots," the defense official told AFP on condition of anonymity.

Source: AFP