The powerful sister of North Korea’s leader has vowed to retaliate against South Korea after Seoul resumed loudspeaker propaganda broadcasts at the heavily militarized border for the first time in years.

Kim Yo Jong said late Sunday that Seoul would bear witness to a “new counteraction” following the restart of the loudspeaker broadcasts and activists’ floating of balloons carrying antiregime leaflets and USB sticks loaded with South Korean dramas and music across the border, a move the South cannot legally stop.

The North Korean regime fears the loudspeaker and leaflet campaigns since they provide front-line troops and residents with information that could weaken its grip on power and has demanded that Seoul take action.