North Korea on Saturday demanded that the South halts anti-North propaganda broadcasts via loudspeakers along the border or face military action, a day after it denied Seoul's accusation that it planted landmines that wounded two South Korean soldiers.
Tension on the Korean peninsula has escalated since the landmine explosion last week and as the US and South Korean militaries prepare to begin annual joint exercises.
South Korea has threatened counter-measures and began using loudspeakers to blare anti-Pyongyang rhetoric across the border on Monday, resuming broadcasts that had been suspended since 2004.
South Korea's defence minister told the parliament on Thursday that Seoul would expand the scale of the broadcasts to all frontline bases, and planned to remove trees along the Demilitarised Zone (DMZ) to get a better view.
"The resumption of the broadcasting is a direct action of declaring a war against the DPRK," the Front Command of the Korean People's Army said in a statement on Saturday carried by the state KCNA news agency. North Korea's official name is the Democratic People's Republic of Korea.
Failure to halt the broadcasts would result in military action "to blow up all means for 'anti-north psychological warfare'," along the front, it warned.
"They should not forget that the KPA military action means indiscriminate strikes which envisage even possible challenge and escalating counteraction," it said.
South Korean President Park Geun-hye said Seoul would respond to any provocation.
"Provocations and threats only lead to isolation and destruction," she said during a speech marking the 70th anniversary of the end of Japanese colonial rule on the Korean peninsula.
"But if North Korea chooses the path of dialogue and cooperation, it can grab an opportunity of improvement of livelihood and economic development."
US and South Korean forces on Monday begin annual joint military exercises, which Pyongyang condemns as a preparation for war.
North and South Korea are technically still at war as the 1950-1953 Korean War ended in an armistice, not a peace treaty.
The DMZ is a 4-km (2.5-mile) wide buffer fortified with landmines and barbed wire stretching across the Korean peninsula, with more than a million soldiers and heavy military equipment deployed on both sides.