South Korea must put a stop to activists sending leaflets across the border into North Korea, a top official said Thursday, warning that Pyongyang could withdraw from an important inter-Korean military agreement should the "anti-DPRK" activity not come to an end.

In a statement carried in both party daily the Rodong Sinmun and the Korean Central News Agency (KCNA), Kim Yo Jong, the powerful sister of the North Korean leader lashed out at Seoul for failing to stop a group of defectors from dropping tons of leaflets into the North late last month.