SEOUL, South Korea (AP) — South Korea’s military fired warning shots, scrambled fighter jets and flew surveillance assets across the heavily fortified border with North Korea on Monday, after North Korean drones violated its airspace for the first time in five years in a fresh escalation of tensions.

South Korea’s military detected five drones from North Korea crossing the border, and one traveled as far as the northern part of the South Korean capital region, which is about an hour’s drive away, South Korea’s Joint Chiefs of Staff said.

The military responded by firing warning shots and launching fighter jets and attack helicopters to shoot down the North Korean drones. The attack helicopters fired a combined 100 rounds but it wasn’t immediately known if any of the North Korean drones were shot down, according to the Defense Ministry.