SEOUL (Reuters) -South Korea will face "devastating consequences" for dropping anti-Pyongyang leaflets over North Korea, state media KCNA said on Tuesday, citing Kim Yo Jong, North Korean leader Kim Jong Un's powerful sister.

At least 29 large balloons carrying anti-Pyongyang leaflets from South Korea were found around North Korea, prompting a blockade in the areas and causing inconvenience to residents, Kim said.

Tension flared last month after North Korea sent thousands of balloons containing trash to the South in protest against a campaign by North Korean defectors and activists in the South who have for years flown aid parcels and leaflets criticising the Kim regime across the heavily fortified border.

Kim said Pyongyang might respond differently if "petty and dirty" behaviour by what she called "human scum" continues, without elaborating.

"The situation seemed to be becoming unacceptable. Again I give you a stern warning," she said in a statement carried by KCNA. "You will have to face devastating and horrible consequences."

(Reporting by Hyonhee Shin; Editing by Jacqueline Wong and Lincoln Feast.)