“An analysis of the camera memory (of the drone) found pictures of Seongju where THAAD is deployed. (We believe the drone) began taking pictures several kilometers north of Seongju and headed south to the THAAD battery site,” a JCS official said on the condition of anonymity.

Equipped with a Sony digital camera, the drone reportedly had more than 250 pictures, mostly of forest and villages. The pictures of Seongju were clear enough to make out two THAAD launchers and its radar installed, the official added.

The incident could be a staged show with the deliberate intention to provoke the allies, rather than a real spy activity, the JCS official said, adding that the drone appears to be lacking the technology to transmit the imagery back to the North.

“We are trying to figure out whether the North intended to provoke (the allies) as it did in 2014,” said the official, adding that the military is currently trying to find out whether there are additional drones sent from the North.

North Korea has flown spy drones before. In 2014, one of them was found to have spied on the presidential residence of Cheong Wa Dae. At that time, the South Korean defense ministry concluded that the drone did not pose “a direct threat” to national security.

Nevertheless, the military has ramped up vigilance against North Korean spying activities, establishing what they call an “integrated system” between the Army and the Air Force to detect and intercept the drones.

But there are still challenges to exactly locate and intercept small-size drones with current surveillance and anti-missile capability, particularly in the border region where battle area is spread out across the Military Demarcation Line, the official added.

“Given that the border region is so broad, it takes time to develop advanced radars and anti-air artilleries fit for the region,” said another JCS official. “We have forward-deployed some anti-missile assets. Although there is a challenge, we did our best.”

The drone, discovered last week, is thought to have traveled more than 500 kilometers before crashing down on a mountain near Injae, Gangwon Provicne. The THAAD battery in Seongju is located about 270 kilometers from the crash site.

The device is bigger than the one that the South has recovered in 2014, the JCS said. It also employs a twin engine, not a single engine used by the previous model, the military added.

By Yeo Jun-suk (jasonyeo@heraldcorp.com)