DUBAI, United Arab Emirates (AP) — A U.S. Coast Guard vessel fired in self-defense on an Iranian boat in the Persian Gulf, the Navy said Wednesday, an encounter that could exacerbate tensions between the two countries as they work to hammer out a lasting deal over Iran’s nuclear program.

Cmdr. Kevin Stephens, a spokesman for the U.S. Navy’s Bahrain-based 5th Fleet, said personnel on a small boat dispatched from the U.S. Coast Guard patrol boat Monomoy fired a single shot when it saw crew on a nearby Iranian dhow training one of its two .50-caliber machine guns on them and preparing to fire.