Three small drones recovered near the inter-Korean border in recent months came from North Korea, South Korea's defence ministry says.
South Korean and US experts reached the conclusion based on data recovered from the unmanned aerial vehicles (UAVs).
Ministry spokesman Kim Min-seok said on Thursday that the finding was "clear military provocation".
Pyongyang had denied owning the drones, which were found in different locations in South Korea between March and April.
Last month, South Korean officials said a preliminary investigation showed that the drones were from the North.
"By analysing the data, the joint investigation team has secured the smoking gun - clear, scientific evidence that all three UAVs originated from North Korea," the defence ministry's Mr Kim said.
He added that all three were "programmed to fly over" military facilities, and that the new military threat required a stern response.
South Korean Vice-Defence Minister Baek Seung-joo described the drones as very rudimentary.
"However, there is always the possibility that the North might use them for attacks after arming them with high explosives, considering its irrational and reckless tendency for provocative acts," he told journalists.
One of the drones found in Paju, just south of the demilitarised zone that separates the two Koreas, had a camera that took pictures of military installations and South Korea's presidential compound, previous reports said.
The two Koreas were divided at the end of the 1950-53 Korean War, which ended in an armistice rather than a peace treaty and they remain technically at war.
North Korea is the subject of multiple UN resolutions relating to its pursuit of nuclear weapons' development.