More than 150 balloons distributed by North Korea carrying apparent propaganda leaflets as well as trash and excrement were detected across South Korea, Seoul's military said Wednesday.

Earlier this week, North Korea vowed "tit for tat action" after human rights activists launched balloons carrying anti-Pyongang pamphlets and USB flash drives filled with South Korean pop culture content into the North.

The balloons crossed the border since Tuesday night, landing in locations across the country, from the capital city to as far as South Gyeongsang Province, according to the Joint Chiefs of Staff. The balloons are reported to have scattered waste as they fell to the ground.

The balloons appeared to have carried various kinds of waste, including plastic bottles, batteries, shoe parts, and even manure. Military officials are currently collecting the debris for detailed analysis.

"These acts by North Korea clearly violate international law and seriously threaten our people's safety," the Joint Chiefs of Staff said. “We sternly warn North Korea to cease its inhumane and vulgar actions immediately.”

The military has reported spotting unidentified objects, believed to be from North Korea, near the demilitarized zone, the heavily fortified border separating the two Koreas.

Authorities have urged the public to avoid approaching these objects and to report any sightings to the military or police immediately, adding that balloons could cause damage as they fall.

The military pledged to devise comprehensive safety measures in collaboration with the police and government agencies, emphasizing its close cooperation with the US-led United Nations Command, which oversees activities in the Demilitarized Zone separating the two Koreas.

Such actions come after North Korea said earlier Sunday, that it will retaliate in response to anti-North Korean leaflets flown across the border to the North.

"Mounds of wastepaper and filth will soon be scattered over the border areas and the interior of the Republic of Korea, and it will directly experience how much effort is required to remove them," Kim Kang-il, the North's vice defense minister, said in a statement released via state media, using the acronym for South Korea's official name.

For years, North Korean defectors in South Korea and conservative activists have sent leaflets in balloons to the North criticizing the regime and urging North Koreans to eventually rise up against the Kim dynasty that has ruled the country for decades.

They have also sent USB memory sticks of K-pop music videos, which are banned in the North.

North Korea has bristled at the propaganda campaign amid concern that an influx of outside information could pose a threat to its leader Kim Jong-un.

The use of propaganda balloons has long been a source of tension between North Korea and South Korea, and Pyeongyang has repeatedly called for an end to the leafleting campaign.

Meanwhile, emergency text messages alerting residents about the unidentified objects caused widespread confusion overnight Tuesday.

The messages, which included the English phrase "Air raid preliminary warning," advised recipients to avoid outdoor activities and to notify the military if they encountered any suspicious leaflets.

The public alert prompted a surge in calls to police and fire authorities from startled residents, who inquired about the authenticity of the alert and whether they needed to evacuate.

Anxious comments were also posted online, particularly regarding the inclusion of the term "air raid" in the message, which typically refers to incoming ordnance rather than ordure.