South Korea accuses the North of launching more trash balloons into its airspace

South Korea on Thursday accused North Korea of launching more trash balloons across the border. 

South Korea's Joint Chiefs of Staff said it had detected around 420 balloons from Wednesday evening to early Thursday. Around 20 of them have been discovered so far in Seoul, the South Korean capital, and nearby Gyeonggi province.

The balloons that landed were filled with paper waste, plastic bottles and other trash but contained no hazardous materials, officials said, accusing the North of launching more balloons into Thursday evening. 

The joint chiefs advised people to report to the police or military if they see any fallen balloons and not to touch them. No major damage was immediately reported.

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Seoul's city government issued text alerts Wednesday evening as the North Korean balloons began appearing over South Korean territory, advising people to stay indoors and to beware of objects dropping from the sky.

The two Koreas have been engaged in petty Cold War-style psychological warfare since at least March, with the North having flown thousands of balloons toward the South, filled with wastepaper, cloth scraps, cigarette butts and even manure. 

North Korea says the balloons are in retaliation against South Korean civilian activists who fly anti-North Korean propaganda leaflets across the border.

Trash carried by at least one North Korean balloon fell on the South Korean presidential compound in July, raising concerns about the vulnerability of key South Korean facilities. Officials said the balloon contained no dangerous materials and that no one was hurt.

South Korea has retaliated with front-line loudspeakers to blast propaganda messages and K-pop songs toward the North.

The tit-for-tat campaigns are adding to tensions fueled by North Korea's growing nuclear ambitions and South Korea's expansion of joint military exercises with the United States.

The Associated Press contributed to this report.