The powerful sister of North Korean leader Kim Jong-un slammed South Korean "scum" on Sunday for launching anti-regime propaganda leaflets across the border via balloon, warning they would pay "a very high price."

The Korean peninsula has seen tit-for-tat balloon campaigns in recent weeks, with Pyongyang floating trash-filled balloons southward in protest of ones carrying propaganda leaflets sent northward by South Korean activists.

Kim Yo-jong, a key regime spokesperson, said she was informed the latest batch of "dirty leaflets and things of the ROK scum" had been found in North Korean territory along the border, according to a statement carried in English by the official Korean Central News Agency.

ROK is an abbreviation of South Korea's official name. North Korean military personnel were "now making an all-out search, throwing into fire and disposing of the found rubbishes," she said.

"Despite the repeated warnings of the DPRK, the ROK scum are not stopping this crude and dirty play," she added, using the initials of the North's official name.

"The ROK clans will be tired from suffering a bitter embarrassment and must be ready for paying a very high price."

Pyongyang has already sent more than a thousand balloons carrying trash southward in what it says is retaliation for balloons carrying propaganda criticising Kim Jong Un's rule. In response, Seoul has fully suspended a tension-reducing military deal and restarted some propaganda broadcasts from loudspeakers along the border.

Relations between the North and South are at one of their lowest points in years, with Pyongyang ramping up weapons testing as it draws ever closer to Russia.

Seoul and Washington have accused Pyongyang of supplying arms to Moscow for use in the war in Ukraine, which would violate rafts of sanctions on both countries.

Earlier this year, the nuclear-armed North declared Seoul its chief enemy, and has jettisoned agencies designed for outreach and diplomacy with Seoul, while ramping up security along the shared border. (AFP)