So far this year, Pyongyang has declared South Korea its "principal enemy", jettisoned agencies dedicated to reunification and outreach, and threatened war over "even 0.001 mm" of territorial infringement.

Pyongyang's latest announcement came after Washington and Seoul started their annual spring military exercises Monday with double the number of troops participating compared to 2023.

The North's live-fire drills on Thursday involved border units "that put the enemy's capital in their striking range," Pyongyang's official Korean Central News Agency (KCNA) said, referring to Seoul.

Kim urged his soldiers to "vigorously push forward the work for making preparations for regular combat mobilisation" to "take the initiative with merciless and rapid strikes" in the event of an "actual war", according to KCNA.

Seoul's military also confirmed the North had carried out live-fire artillery drills involving rocket launchers and self-propelled howitzers.

They took place in North Korea's western port city of Nampho toward the Yellow Sea, it added.

"Our military is closely monitoring North Korea's signs of provocation ... while maintaining a firm joint defense posture and conducting the ongoing Freedom Shield exercises and joint drills," Seoul's Joint Chiefs of Staff said in a statement.

"If North Korea commits a provocation, we will punish overwhelmingly and firmly in accordance with the principle of 'immediately, strongly, and until the end'".

North Korea on Tuesday warned that Seoul and Washington would pay a "dear price" over the large-scale military exercises, urging the allies to cease "frantic war drills".

North Korea has long condemned joint US-South Korea military exercises, calling them rehearsals for an invasion.

The nuclear-armed North has in the past carried out weapons tests as a response to such joint exercises.

As he watched the drills on Thursday, Kim "expressed his great satisfaction" that the units are "fully ready for constant mobilization for battles," according to KCNA.

On Wednesday, he visited a major operational training base in the country's western region, with photos released afterward showing him talking with troops and overseeing firing drills.

Last week, South Korea's hawkish President Yoon Suk Yeol called for the international community to back "unification efforts" to "free" everyone on the peninsula.