South Korea has been forced to repeatedly shut down runways at the two main airports for the capital Seoul since June due to disruption from balloons carrying trash launched by North Korea, a South Korean lawmaker said on Wednesday,

North Korea’s trash-laden balloons interrupted operations at Seoul-area airports 20 times this year. As of Monday, trash balloons had disrupted air traffic for a combined 413 minutes at Incheon International Airport and Gimpo International Airport.

Over the weekend, North Korea launched a further batch of balloons carrying waste across the border, causing chaos in the south and provoking anger from Seoul officials. The response from South Korea signals that the heightening tensions between the two may soon spill over into a more significant confrontation.

The powerful sister of North Korean leader Kim Jong Un has vowed to boost the country’s nuclear war capability and take other steps to protest the recent arrival of a U.S. nuclear-powered submarine in South Korea.

Mounds of wastepaper and filth will soon be scattered over the border areas and the interior of the ROK [South Korea] and it will directly experience how much effort is required to remove them.’