South Korea has said it has proof North Korea flew spy drones into its territory in a "clear military provocation", after an analysis of the wreckage of three crashed vehicles.
Kim Min-seok, a spokesman for the South's defence ministry, said the provenance of the unmanned aerial vehicles was confirmed after a joint South Korea-US study of the GPS coordinates stored in their systems.
North Korea's action is a clear military provocation that violates the armistice and the South-North non-aggression agreement.
The drones were recovered from three separate locations near the inter-Korean border between March 24 and April 6, the ministry said.
"We have confirmed that all three UAVs originated from North Korea," Kim said.
"North Korea's action is a clear military provocation that violates the armistice and the South-North non-aggression agreement," the ministry said in a statement.
One crashed due to an engine problem, while the other two ran out of fuel.
Although extremely rudimentary in design, they were all equipped with cameras and had taken pictures of border areas, major military installations and the capital Seoul, including the presidential palace.
North Korea has denied any connection to the drones, and accused Seoul of fabricating a link in order to smear Pyongyang.
Photographs unearthed by the North Korea Tech blog showed a drone made by a Chinese company with an almost identical size and shape to some of the drones found in South Korea, the Reuters news agency reported.
South Korea's defence ministry said in April some of the parts in the recovered drones were made in China, Japan, the Czech Republic and the US, but it offered no further details.
The South in 2011 said it wanted to buy drone vehicles from the US. In 2012, the US agreed to sell Seoul four "Global Hawk" spy drones, after the Obama administration vowed to help the South counter its northern rival.
Arms control advocates expressed fears that the deal would increase instability and stir a regional arms race, as well as provide diplomatic cover for an expansion of such exports by Russia, China and others.
North Korea had displayed a set of basic drones during a military parade held in Pyongyang last July marking the 60th anniversary of the end of the Korean war.
In March 2013, state media reported leader Kim Jong-un overseeing a military drill using "super-precision drone planes".
Photographs of the exercise, broadcast on state television, showed what resembled air force target drones being flown into a mountainside and exploding.