SEOUL, South Korea (AP) — North and South Korea traded machine-gun and rifle fire Friday after South Korean activists released anti-Pyongyang propaganda balloons across the border, officials said, a sudden reminder of the bitter rivals’ animosity despite some recent glimmers of trust-building.

North Korea opened fire nearly two hours after the release of the balloons, Defense Ministry spokesman Kim Min-seok said, and several 14.55 mm machine gun bullets fell south of the border near a South Korean base and a residential area. Kim said South Korea then fired 40 rounds from K-6 machine guns. The North then opened fire with rifles, which South Korean soldiers responded to in kind, Kim said. There were no reports of damages or injuries. It wasn’t immediately clear if North Korea was firing at the balloons.