North Korea has launched hundreds more rubbish-filled balloons towards the South after a similar campaign a few days earlier, according to South Korea’s military, in what Pyongyang called retaliation for activists flying anti-North Korean leaflets across the border.

Between Saturday night and Sunday morning, about 600 balloons flown from North Korea have been found in various parts of South Korea.

The balloons carried cigarette butts, scraps of cloth, waste paper and vinyl, but no dangerous substances were included, South Korea’s Joint Chiefs of Staff said on Sunday.

The military advised people to beware of falling objects and not to touch objects suspected to be from North Korea but to report them to military or police offices instead. There have been no reports of injuries or damage.

In Seoul, the city government sent text alerts saying that unidentified objects suspected to have been flown from North Korea had been detected in skies near the city and that the military was responding to them.

The North’s balloon launches added to a recent series of provocative steps, which include its failed spy satellite launch and a barrage of short-range missile launches that the North said was intended to demonstrate its ability to attack the South pre-emptively.

South Korea’s military dispatched chemical rapid response and explosive clearance teams to recover the debris from some 260 North Korean balloons that were found in various parts of the country from Tuesday night to Wednesday.

The military said the balloons carried various types of rubbish and manure but no dangerous substances like chemical, biological or radioactive materials. Some of the balloons were found with timers which suggested they were designed to pop mid-air.

In a statement on Wednesday, Kim Yo Jong, the powerful sister of North Korean leader Kim Jong Un, confirmed the North had sent the balloons to make good on her country’s recent threat to “scatter mounds of wastepaper and filth” in South Korea in response to leafleting campaigns by South Korean activists.

She hinted that balloons could become the North’s standard response to leafletting, saying the North would respond by “scattering rubbish dozens of times more than those being scattered to us”.

South Korea’s Unification Ministry said on Friday that North Korea must stop the provocations – also including its missile launches and other acts – or face unspecified “unbearable” consequences.

South Korea’s military has said it has no plans to shoot down the balloons, citing concerns about causing damage or the possibility that they might contain dangerous substances. Firing at balloons near the border would also risk triggering a retaliation from the North at a time of high tensions.

“(We) decided it was best to let the balloons drop and recover them safely,” Lee Sung Joon, of South Korea’s Joint Chiefs of Staff, said during a briefing on Thursday.

North Korea is extremely sensitive about any outside attempt to undermine Kim Jong Un’s absolute control over the country’s 26 million people, most of whom have little access to foreign news.

In 2020, North Korea blew up an empty South Korean-built liaison office on its territory after a furious response to South Korean civilian leafleting campaigns.

In 2014, North Korea fired at propaganda balloons flying towards its territory and South Korea returned fire, though there were no casualties.

In 2022, North Korea even suggested that balloons flown from South Korea had caused a Covid-19 outbreak in the isolated nation, a highly questionable claim that appeared to be an attempt to blame the South for worsening inter-Korean relations.