South Korea's Defense Ministry announced Thursday that three small drones found near the inter-Korean border in March and April were all sent from North Korea, Yonhap News Agency reported. The ministry said a team of South Korean and American experts had confirmed the origin of the drones after restoring the coordinates of the geographical positioning system (GPS) stored in their system. "All three unmanned aerial vehicles originated from North Korea and were programmed to return to the same regions," Kim Jong-seong, the director of the state-run Agency for Defense Development, said in a briefing at the defense ministry. The announcement came about a month after an interim investigation pointed the finger at Pyongyang for sending the small unmanned aerial vehicles to South Korea based on circumstantial evidence. One unmanned aerial vehicle was discovered in Paju, north of Seoul, on March 24, while another was found on a western border island a week later. The third drone was found in a mountain near the east coast on April 6. The drones, equipped with a camera and a parachute, departed from North Korea and flew southward to prearranged coordinates to take photos of key facilities and military installations along their routes. Although the devices were programmed to return to their departure point, they failed to complete their mission. One crashed due to an engine problem, while the other two failed due to fuel shortage, Kim said. "All three drones were ordered to fly over South Korea's military facilities according to the prearranged data," Kim said. Paju drone took photos of key installations in Seoul metropolitan area, including the presidential office in the capital city, while Baengnyeong Island drone took photos of troops on two western border islands. North Korea is believed to have made the drones based on Chinese unmanned aerial vehicles it had acquired via Hong Kong. The South Korean military has asked the Chinese Embassy to figure out the link between the Chinese manufacturer with North Korea, the report said. Seoul condemned Pyongyang for border incursions by the spy aircraft. The two Koreas are technically at war as the 1950-53 Korean War ended in a ceasefire, without signing a peace treaty. In light of the border incursions by North Korea's spy aircraft, the South Korean military vowed to step up air security by acquiring low-altitude surveillance radars and other strike weapons.