'Dirty things': North Korea drops trash-filled balloons on South Korea

North Korea sent about 150 garbage-and-excrement-filled balloons flying toward South Korea on Wednesday, state media reported, prompting officials to warn residents to stay inside.

The incident, reported by the South's official Yonhap News Agency, citing military sources, comes as the North had vowed in recent days to retaliate against its neighbor after Seoul-based political activists earlier this month launched propaganda-filled balloons across the heavily fortified border in the direction of Pyongyang.

The two Koreas have been divided since the Korean War ended in 1953. However, they are technically still at war because they only agreed to a cease-fire and never signed a formal peace treaty. Both sides have been using balloons and even message-filled bottles floating down a border river as part of their information war for years.

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Photographs released by the South's military and others shared on social media on Wednesday showed inflated balloons with plastic bags tethered to them. Some appeared to be filled with toilet paper, dark soil and batteries. Other images showed deflated balloons, with the word "excrement" written on them.

"These acts by North Korea clearly violate international law and seriously threaten our people's safety," the South's military said. "(We) sternly warn North Korea to immediately stop its inhumane and vulgar act."

Authorities advised people who live north of Seoul's capital to "refrain from outdoor activities." A military explosives ordnance unit trained in chemical and biological warfare was dispatched to inspect the balloons.

The balloons floated toward the North earlier this month carried information about the South's democratic society, leaflets that criticized the North's leader Kim Jong Un and USB memory sticks with clips from popular news shows and television dramas, as well as Korean pop music videos. All are banned in the North.

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The North gave advance warning on Sunday that it would respond.

"Mounds of wastepaper and filth will soon be scattered over the border areas," in response to the "dirty things" sent toward Pyongyang, the North's Deputy Defense Minister Kim Kang II said in a statement.

This article originally appeared on USA TODAY: North Korea drops trash balloons on South Korea