The drone crashed on Baengnyeong island on Monday when the two Koreas fired hundreds of artillery shells into each other's waters in a flare-up of animosity over a long-disputed sea boundary between the countries. No one was reported injured and all the shells splashed into the water.
Presidential spokesman Min Kyung-wook told South Korean reporters that Seoul officials think the drone is from North Korea based on a preliminary investigation, according to his office. The spokesman didn't elaborate.
Last week, another unmanned drone was found in a South Korean city near the land border with North Korea. Media reports said South Korean officials suspect this drone was also flown by North Korea and that it took pictures of the South Korean presidential office and a highway linking border areas to Seoul.
The Defence Ministry couldn't confirm the reports, saying officials were still investigating the two drones.
The two Koreas have been divided along the world's most heavily fortified border since the 1950-53 Korean War ended with an armistice, not a peace treaty.