A drone, which had been photographing a controversial US missile defence shield, was discovered early June after it crashed close to a sensitive military installation along the heavily fortified border, Seoul's military said.
"The latest action by the North... is a grave provocation and a wanton violation of the armistice," Jeon Dong-Jin, first deputy director of the South's Joint Chief of Staff, told reporters, referring to the treaty which ended the 1950-53 war.
A full investigation into the drone's wreckage discovered its planned itinerary and confirmed that it had taken off from the North before capturing more than 500 photos of the South's territory, the defence ministry said.
"We strongly condemn the North's series of drone provocations and urge it to stop all such provocations immediately," Jeon said, vowing "strong retaliation" against any further actions by Pyongyang.
The South has requested an investigation by the UN Command which is in charge of supervising the armistice, which ended open conflict between the two sides, but has never been replaced with a final peace treaty.
Seoul's military said it was beefing up the country's defense against potential spying activities -- or even future attacks -- by North Korean drones, adding more border surveillance radars and anti-aircraft guns to shoot down drones.
Photos retrieved from the latest drone include several overviews of the site for the Terminal High Altitude Area Defense (THAAD) system in the southeastern county of Seongju, according to the military.
The powerful US anti-missile system was installed this year to guard against growing missile threats from the nuclear-armed North.
South Korea in recent years has repeatedly accused the North of flying suspected spy drones across the tense border bisecting the peninsula.
In 2014, crashed drones equipped with cameras containing images of South Korean military facilities were found at the border region. The South's military blamed the North for the incursions.
A year later, South Korea triggered an anti-aircraft warning and sent an attack helicopter and fighter jet to track down a drone that crossed the border.
In January last year, South Korean soldiers fired warning shots at a suspected North Korean drone that flew across the western part of the border.
South Korea's new President Moon Jae-In this month urged the military to establish a system to efficiently deal with the North's drones.
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