REPUBLIKA.CO.ID, SEOUL -- North Korea has scattered nearly one million propaganda leaflets in South Korea over the past week, Seoul said Monday, in an escalating propaganda battle triggered by Pyongyang's latest nuclear test.

The leaflets, floated across the border by helium balloons, are an apparent response to South Korea's decision to blast a mix of K-pop and propaganda messages into North Korea using giant banks of speakers on the heavily militarised border.

North Korea has retaliated with its own loudspeaker broadcasts along with the leaflets attacking South Korean President Park Geun-hye.

The tit-for-tat exchanges are the result of the North's fourth nuclear test carried out -- to near universal condemnation -- on January 6.

The defence ministry said the North's leaflets were being air-dropped on a near daily basis and estimated the number that had been scattered at close to one million.

Most have been recovered near the border in Gyeonggi province, though some have made it as far as Seoul.

A ministry official told AFP that the North was using helium balloons with timers that cause them to explode and scatter the leaflet packages.

It can be a blunt propaganda tool. Last week an unopened package of nearly 10,000 leaflets slammed into a car, imploding the roof.

Yang Moo-Jin, a professor at the Seoul-based University for North Korean Studies, said the leafleting was largely a reactive gesture.

"They couldn't just sit idle while South Korea launches a psychological warfare front," Yang said.

As well as the loudspeakers, Seoul is considering installing giant electronic signboards on the border to display messages and videos.

South Korea halted official leaflet drops following an inter-Korean agreement reached in 2004, but civic groups have kept up balloon launches into the North for years -- much to Pyongyang's annoyance.

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