South Korea said Tuesday a drone believed sent from North Korea had been spying on a US missile defence system before it crashed.
The remains of the small drone, which was equipped with a camera, were retrieved by the South's military last week from a hillside where it had crash-landed close to the heavily-fortified inter-Korean border.
The military analysed the contents of the camera's 64-gigabyte memory chip and said it had been spying on the missile defence system known as the Terminal High Altitude Area Defense (THAAD).
"It has been confirmed that it took photos of the THAAD site in Seongju," a defence ministry official told journalists Tuesday.
He said they had "high suspicions" that the drone was from North Korea as it was similar to previous drones sent across the border by Pyongyang.
The drone, which was flying at an altitude of between two and three kilometers, started photographing a few kilometers north of the South's southeastern county of Seongju. It swept over the site before making a U-turn a few kilometers south of the site, the official said.
Of the hundreds of photos on the memory chip, at least 10 were an overview of the THAAD site.
"Two missile launchers and the fire control radar of the system which have already been deployed were also included in the pictures," he added.
Seoul agreed last year to deploy the missile interceptor system to guard against threats from nuclear-armed North Korea, despite angry opposition from China -- which believes THAAD could undermine its own military capabilities.
Two missile launchers are already in place but Seoul has decided to suspend any further deployment until an environmental impact assessment ordered by new President Moon Jae-In is finished.
South Korea has repeatedly accused the North of flying suspected spy drones across the tense border.
In January last year South Korean soldiers fired warning shots at a suspected North Korean drone that crossed the western part of the border, the most sensitive part of the Demilitarised Zone.
In September 2015 South Korea triggered an anti-aircraft warning and sent an attack helicopter and fighter jet to track down a drone that crossed the border, without success.
A year earlier a South Korean fisherman found the wreckage of a North Korean drone in his net near a frontline island south of the rivals' disputed Yellow Sea border.
A few months previously, crashed drones equipped with cameras were found in three different places near the border.
After a joint investigation with US experts, Seoul said they were flown from North Korea and had been pre-programmed to fly over South Korean military installations..