North Korea's unmanned attack drones are believed to be capable of striking all targets in South Korea, a government official said Sunday, amid new security concerns over North Korea's spy drones.

North Korea has deployed unmanned attack drones it unveiled in March last year during military drills meant to destroy low-flying cruise missiles and test the accuracy of unmanned combat aerial vehicles.

The range of unmanned attack drones is estimated at up to 800 kilometers, capable of striking major South Korean and U.S. military targets in South Korea, the official said.

About 28,500 U.S. troops are stationed in South Korea, a legacy of the 1950-53 Korean War, which ended in a cease-fire, not a peace treaty.

The comments came as South Korea is pushing to step up its air defense following the recent border incursions by North Korea's spy drones.

Defense Minister Kim Kwan-jin said Friday that Pyongyang could develop more advanced unmanned aerial vehicles for attack purposes, though the two small aircraft, equipped with small cameras, recently found near the inter-Korean border were rudimentary spy drones.

The South Korean military said it is considering purchasing advanced low-altitude surveillance radars and anti-aircraft guns to better detect small aircraft and shoot them down.

In March last year, North Korean leader Kim Jong-un lauded the accuracy of unmanned attack drones and expressed satisfaction with his military's ability to counter U.S. Tomahawk cruise missiles with surface-to-air rockets.

Kim said at that time that he would issue orders to destroy military and government targets in South Korea if provoked, and warned the country could raze U.S. bases all across the Pacific to the ground.

 "The planes were assigned the flight route and time with the targets in South Korea in mind, Kim Jong-un said, adding with great satisfaction that they were proved to be able to mount super precision attack on any enemy targets," the North's official Korean Central News Agency reported in March last year. (Yonhap)