The South Korean military, on Wednesday, said it had detected about 260 balloons filled with animal waste and garbage dropped on the country’s busy streets in front of residences by neighbours North Korea.

The South Korean military released pictures of garbage strewn across streets, including in the country’s capital, Seoul. Some of the items were mixed with a yet-to-be-identified brown substance.

According to local media in South Korea, the balloons were seen at Jeolla Province, near the southern tip of South Korea’s mainland, indicating that the balloons had already spread around the country.

Describing the act as an “inhumane and low-level” act, the South Korean military, in a statement, said the actions violate international law and seriously threaten public safety.

North Korea’s action was in retaliation to the launching of balloons carrying anti-North Korea pamphlets and USB flash drives filled with South Korean pop culture content into the North by a prominent human rights activist.

South Korean officials had dismissed its activists’ action, saying they can’t be blamed for their inability to stop South Korean activists from launching leaflets into the North.

Text messages were sent on Wednesday to South Korean residents in border provinces, warning them against outdoor activities due to unknown objects from their neighbours.

North Korean officials, however, made good their threat to take a “tit for tat action”, while Kim Yo Jong, the sister of North Korean leader Kim Jong Un, in a statement published in the state-run Korean Central News Agency on Wednesday, sarcastically mocked South Korea.

She described balloons containing animal waste and other garbage, as a “genuine ‘gift of sincerity’” and an act of “freedom of expression” on from the North Korean people, and warned that North Korea will respond to such leaflet launches by sending “dozens of times” more balloons into the South in the future.