Parasites from human waste and defaced Hello Kitty clothing have been found in bags of rubbish carried by North Korean balloons into South Korea, officials say.

More than 1,500 waste-carrying balloons have been released by Pyongyang across the border since May, in retaliation for a leaflet campaign sent northwards by opponents of North Korean leader, Kim Kong Un.

Analysis of some of the balloon packages detected “roundworms, whipworms and threadworms” in the soil.

The chance of infection from the parasites in the packages is low, South Korea’s ministry of unification assured people.

Other items carried by the balloons included slashed “western” clothes that had been donated from the South – including items featuring Mickey Mouse, Winnie the Pooh, and Hello Kitty characters, according to Reuters news agency. There were also socks, clothes and heavily patched-up children’s clothes.

The waste sent by North Korea also revealed the country’s woeful economic state, and highlighted “the adversarial stance against South Korea”, a ministry official said.

The soil was probably infected with the parasites because human faeces was used instead of chemical fertilisers in the North, the ministry added.

North Korea says the balloons are retaliation for a propaganda campaign by North Korean defectors and South Korean activists who regularly send balloons the other way, carrying food, medicine, cash and leaflets criticising the North’s regime.

The two Koreas have recently stepped up their cross-border tit-for-tat propaganda war. As the north sent trash floating southward, the south has also been blasting pop songs and news items over the border from powerful loudspeakers.

Monday saw another set of balloons sent across the border, with South Korean officials warning people to beware of falling objects.

An activist in the South told the AFP news agency that he had this week floated more balloons carrying propaganda leaflets towards the north.

South Korea’s military recently cautioned the public against touching the white balloons and the plastic bags attached to them because they contain “filthy waste and trash”.

The recent raft of balloons began in May, when at least 260 balloons carrying rubbish dropped in South Korea, prompting authorities to warn its residents to stay indoors.

In addition to anti-Pyongyang propaganda, activists in South Korea have previously launched balloons carrying items including cash, banned media content, and even Choco Pies – a South Korean snack banned in the North.

In May, a South Korea-based activist group claimed it had sent 20 balloons carrying anti-Pyongyang leaflets and USB sticks containing Korean pop music and music videos across the border.