North Korea released more than 250 balloons carrying animal faeces, toilet paper and rubbish over its southern border on Wednesday. South Korea condemned the “inhumane” attack as “low class” and “vulgar”.

Residents living along the border zone were warned to not touch the suspicious objects. Many received text messages from their provincial authorities asking them to “refrain from outdoor activities”.

The balloons were found in eight of the nine provinces in South Korea and reached as far as the south-eastern province of South Gyeongsan.

Photographs shared across South Korean media showed rubbish bags tethered to large white balloons floating above fields and roads. The media said that the balloons were carrying “filthy waste and rubbish”.

Several balloons and bags were pictured having burst upon landing, with their contents splattered across cars, gardens, and roads. Plastic bottles, batteries, shoe parts and manure were spotted among the debris.

The South Korean military’s explosives ordnance unit and chemical and biological warfare response teams have been dispatched to analyse the contents.

Seoul’s Joint Chiefs of Staff confirmed that the “unidentified objects” came from Pyongyang after being first launched on Tuesday night.

It added: “This move by North Korea is a clear violation of international law and seriously threatens the safety of our people. We sternly warn the North to immediately stop its inhumane and vulgar actions.”

Over the weekend, Kim Kang Il, North Korea’s vice defence minister, had warned that the regime would fly “mounds of wastepaper and filth” into the South in response to propaganda leaflets being sent by Seoul-based activists.

The balloon campaigns is often a tactic from South Korea, where North Korean defectors and human rights groups in Seoul often drop leaflets criticising the regime across the border. The leaflets often urge North Koreans to rise up against the Kim dynasty that has ruled the country for decades.

They sometimes include flash drives with videos of K-pop or Korean dramas, which are banned in the North.

It is the latest incident in simmering tensions between the neighbouring countries that have technically been at war since the 1950-53 Korean War ended in an armistice.

Peter Ward, a research fellow at the Sejong Institute, said sending balloons was far less risky than taking overt military action.

He said: “These kinds of grey zone tactics are more difficult to counter and hold less risk of uncontrollable military escalation, even if they’re horrid for the civilians who are ultimately targeted.”

In 2022, Pyongyang blamed South Korean balloons for a large-scale coronavirus outbreak in the country, attributing a surge in cases to “alien things coming by wind”.