A U.N. investigation into a recent exchange of gunfire between the two Koreas has determined that both countries violated the armistice that ended the 1950-53 Korean War, the American-led U.N. Command said Tuesday. The May 3 gunfire exchange was the first shooting inside the Korean Demilitarized Zone in about 2½ years. The DMZ, which was established as a buffer at the end of the Korean War, is a de facto border separating North and South Korea.