Seoul's Joint Chiefs of Staff said that "unidentified objects believed to be North Korean propaganda leaflets have been identified in the Gyeonggi-Gangwon border area and the military is taking action".
"Citizens should refrain from outdoor activities, do not come into contactwith any unknown objects, and report them to the nearest military base orpolice," it said in a statement sent to AFP.
Late Tuesday night, Gyeonggi province issued a text message alert toresidents.
"Refrain from outdoor activities and report (objects from North Korea) tomilitary bases when identified," it said in the message.
Since the 1950-53 Korean War ended in an armistice, the two Koreas remain technically at war and are separated by a heavily fortified border includingthe Demilitarised Zone (DMZ), reports BSS.
South Korean activists sometimes release balloons carrying anti-Kim Jong Unregime propaganda leaflets and money intended for people living north of theborder.
Pyongyang has long been infuriated by such propaganda campaigns, possibly dueto concerns that an influx of outside information in the tightly controlledsociety could pose a threat to the Kim regime.
On Sunday, North Korea warned it would retaliate in a statement carried by the official Korean Central News Agency.
"Tit-for-tat action will be also taken against frequent scattering ofleaflets and other rubbish by the ROK near border areas," Kim Kang Il, avice-minister of defence, said in the statement, using the acronym for South Korea's official name.
"Mounds of wastepaper and filth will soon be scattered over the border areasand the interior of the ROK and it will directly experience how much effortis required to remove them," Kim said.
- 'Toilet paper, trash' -
North Korea has sent propaganda balloons across the border before, in 2016 for example, but their approach is a bit different this time, Cheong Seong-chang of the Sejong Institute told AFP.
"Bags filled with toilet paper, trash and Chinese batteries were found," hesaid.
"Also from witness statements that there was a 'distinctive smell' from the bag, it is likely they sent faeces, probably animal faeces, as well," headded.
Local media reports carried photographs purportedly showing balloons carryingbags of what appeared to be trash.
"It's a stern message to South Korea that like the South, North Korea cansend propaganda as well, and they should immediately stop doing it," Cheongsaid.
"The border will be strongly controlled after this," he added.
North Korea on Monday attempted to put a second spy satellite into orbit, butthe launch ended in a mid-air explosion.
Seoul has slammed the launch, and conducted drills with fighter jets inprotest, after Pyongyang informed Tokyo of the pending launch window earlierthis week.
North Korea's Kim said that Seoul's response was "recklessness" according toa KCNA report Wednesday.
Kim said "the present situation requires further bolstering up the wardeterrence in every way and steadily developing the DPRK's armed forces intoan entity of super-powerful and absolute strength," the report said.