The Navy scoured waters off Korea's east coast following a citizen's report of an object that appeared to be a submarine, possibly from North Korea, but the search turned up nothing unusual, officials said.
A 39-year-old tourist reported to authorities he saw a strange object emerging and then disappearing in waters some 500 meters away from Gyeongpodae beach in Gangneung, about 240 kilometers east of Seoul, around 6:20 a.m. while taking pictures of the sun rising.
The Navy immediately sent an anti-submarine vessel, a PC-3 patrol aircraft and a Linx helicopter to search the area, but no unusual object was located and the operation was wrapped up around 11 a.m., a Joint Chiefs of Staff official said.
The tourist reported an unidentified object in a picture taken with his mobile phone camera looked like a submarine, but a close examination of the photo concluded it is believed to be of a fishing boat, the official said.
"We've determined that the shape of the object was different from that of a submarine," a military official said. "A boat can look like that if a photo is taken when it goes up and down" between swells at sea.
Gangneung is where a North Korean submarine was found stranded in 1996. That triggered a massive manhunt for 25 North Korean sailors and agents who came ashore after abandoning their disabled submarine.
Most were shot and killed though a few were believed to have made it back to the North.
In 2010, a North Korean submarine torpedoed and sank a South Korean warship in waters off the tense Yellow Sea border between the two Koreas, killing 46 sailors aboard the vessel.
Tension near the border has escalated recently after North Korean fishing boats made a series of violations of the maritime boundary, with the South's Navy firing a barrage of warning shots last month to chase the Northern vessels away. (Yonhap)