South Korea said Wednesday it would take legal action against two defector groups for sending anti-Pyongyang leaflets across the border, after North Korea ramped up its threats over the campaigns.

North Korea has issued a series of vitriolic denunciations of the South since last week over activists sending anti-Pyongyang leaflets across the border.

The leaflets -- usually attached to hot air balloons or floated in bottles -- criticise North Korean leader Kim Jong Un over human rights abuses and his nuclear ambitions.

The two groups of North Korean defectors had "violated an agreement between the leaders of the North and the South and created tension," Seoul's unification ministry added in a statement.

It said it would file a legal complaint with the police against them for violating a law on inter-Korean cooperation, and also begin a process to retract their licenses.

Anti-Pyongyang campaigns by defectors at the border have long been a thorny issue between the two Koreas
Anti-Pyongyang campaigns by defectors at the border have long been a thorny issue between the two Koreas AFP / JUNG YEON-JE

The leaflet campaigns have long been a thorny issue between the two Koreas, but analysts said such legal action could spark an outcry over the possible infringement of the right to freedom of expression.

Officials in Seoul said last week they will consider a ban on leaflet launches just hours after a statement on the campaigns from Kim Yo Jong, the powerful younger sister and key adviser to the North Korean leader.

Calling the defectors "human scum" and "rubbish-like mongrel dogs" who betrayed their homeland, she said it was "time to bring their owners to account" -- referring to the South Korean government.

After threatening to scrap a military pact with Seoul and close a liaison office -- where activities were already suspended -- this week she ordered all communication links cut with South Korea.

The move further raised tensions, with inter-Korean ties at a standstill despite three summits between Kim and the South's President Moon Jae-in in 2018.

The two sides remain technically at war after Korean War hostilities ended with an armistice in 1953 that was never replaced with a peace treaty.

South Korea