North Korea on Wednesday sent a swarm of balloons, loaded with garbage and feces, across the border, triggering air raid sirens in one South Korean border community.

North Korea’s move was evidently a response to South Korean groups that occasionally send balloons with leaflets, music, or videos into the North. On Sunday, Pyongyang warned it was preparing a “tit-for-tat action” that would involve “mounds of newspapers and filth” to retaliate against South Korean pamphleteers.

Late on Tuesday evening, residents of South Korea’s Gyeonggi province near the border village of Panmunjom were startled to see “air raid preliminary warnings” appearing on their cell phones.

“Air raid? I panicked because I thought they were talking about some kind of attack,” an area resident told Radio Free Asia (RFA).

The cell phone alert asked people to report any unidentified flying objects. Gyeonggi officials later apologized for issuing this request in the context of an “air raid” alert, which panicked many people living in the shadow of North Korea’s vast missile and artillery arsenal.

Unidentified objects did indeed begin appearing in the sky overnight. The South Korean Joint Chiefs of Staff (JCS) said it tracked about 260 balloons from North Korea, some traveling as far as Seoul and the southeastern provinces. JCS said it was the largest North Korean balloon release to date.

Those balloons proved to be loaded with trash, North Korean propaganda leaflets, and, in some cases, feces. JCS dispatched military teams to examine each balloon payload for biological or radiological contamination, advising residents to refrain from outdoor activities and avoid touching mysterious objects until they have been inspected.

The owner of a vineyard in South Korea’s Yongcheon awoke Wednesday morning to hear a “thumping sound” from one of his greenhouses. When he investigated, he found a heap of plastic garbage and filth dumped by a North Korean balloon had damaged the greenhouse.

Other farmers reported finding bags of North Korean garbage strewn across rice fields and stuck in power lines.

South Korean media carried photos of large white balloons, sometimes several balloons tethered to a large payload. Some of the balloons landed rough, causing their bags of garbage to burst and scatter across the ground.

The JCS said North Korea’s actions “clearly violate international laws and seriously threaten the safety of our people.”

“We sternly warn the North to immediately stop its inhumane and low-class actions,” the South Korean statement said.