South Korea has warned residents living near the border with North Korea to be on alert after media reports said more than 90 balloons carrying various objects including what appeared to be trash and excrement had been detected.
South Korea's military said unidentified objects believed to be from North Korea were seen near the heavily fortified border and urged people to keep away and report them to the military or police.
By Wednesday, more than 90 balloons had been detected, with some landing on the ground, while others were still in the air, Yonhap News reported, citing a military source.
Photographs published in South Korean media showed an inflated white balloon with a plastic bag tethered to it and in another image what appeared to be a collapsed balloon with trash strewn around it.
North Korea's vice defense minister issued a statement on Sunday vowing to exercise "strong power for self-defense" and warned that "mounds of waste-paper and filth" would be sent to the South in response to its flying "dirty things" to the North.