In a photo taken in 2018 a South Korean soldier stands before a security fence at a guard post inside the Demilitarized Zone (DMZ) near the Military Demarcation Line separating North and South Korea. The two sides agreed that year to eliminate guardposts but Pyongyangnow vows to remilitarize the border. Photo: AFP/ Yelim Lee

North Korea’s army is “fully ready” to take action against the South, state media said Tuesday in the latest verbal saber-rattling from Pyongyang, days after its leader’s sister threatened military moves against Seoul.

The General Staff of the Korean People’s Army (KPA) said that inter-Korean relations were worsening and it had been studying an “action plan” to “turn the front line into a fortress.”

That included re-entering areas that had been demilitarized under an inter-Korean agreement, it added.

South Korean reports said that could mean reintroducing guard posts near the heavily fortified border, which the two Koreas agreed in 2018 to scrap in order to defuse tension.

The North Korean army will also plan to carry out “large-scale leaflet scattering” into the South, the statement said.

Since early June, North Korea has issued a series of vitriolic condemnations of the South over activists sending anti-Pyongyang leaflets over the border – something defectors do on a regular basis.

Last week, it announced it was severing all official communication links with South Korea.

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

On Monday, South Korea’s left-leaning President Moon Jae-in urged the North not to “close the window of dialogue.”

Since Pyongyang condemned leaflet launches, Seoul’s unification ministry has filed a police complaint against two defector groups and warned of a “thorough crackdown” against activists.

Some analysts say Pyongyang may be seeking to manufacture a crisis to increase pressure on Seoul while nuclear negotiations with Washington are at a standstill.

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