North Korea launched 720 balloons across the world’s most heavily armed border overnight Saturday, hitting South Korea with their payloads: plastic bags full of cigarette butts and other trash.

Since last Tuesday, North Korea has sent roughly 1,000 of these trash balloons across the Demilitarized Zone separating the two Koreas. Once​ the balloons reached South Korean airspace, ​their timers released the plastic bags containing assorted rubbish, including scraps of used paper and cloth.

The South Korean military dismissed initial reports that the balloons were carrying human waste, but it did note that some of the trash appeared to be compost.

​So far, the authorities in the South have found “nothing hazardous” in the payloads. On Sunday, the office of President Yoon Suk Yeol accused North Korea of “dirty provocations no normal country would think of.” It said South Korea would start taking “steps that North Korea would find unbearable.”

Its officials indicated that they might switch on their loudspeakers along the inter-Korean border to blare K-pop music, which the North’s leader, Kim Jong-un, has found so threatening that he once called it a “vicious cancer.”

The North has cast the floating offensive as “tit-for-tat action.” It has accused North Korean defectors living in South Korea of “scattering leaflets and various dirty things” over its border counties in recent days.