North Korea vowed "merciless" reprisals on Tuesday after a South Korean military official suggested the isolated Stalinist nation should simply disappear.

Speaking to reporters in Seoul on Monday, Defence Ministry spokesman Kim Min-Seok had argued that North Korea barely deserved to be regarded as a proper country and that it would be best if it "vanished as soon as possible."

South Korean officials tend to be guarded in their criticism of the North, and Kim's remarks were seen as unusually blunt and forthright.

The North's powerful National Defence Commission accused Kim of speaking for South Korean President Park Geun-Hye to inspire an "all-out" inter-Korean confrontation.

It warned that North Korea would take strong retaliatory action against anyone who slanders its leadership and system, describing Park and South Korean military officials as "the root of evil".

"Our army and people will wipe them out entirely with the most merciless and thorough striking force," the commission said in a statement carried by the official Korean Central News Agency.

The North's official website Uriminzokkiri, which distributes news and propaganda from the state media, warned earlier that Kim should pay a "steep" price for his remarks.

The two Koreas have upped the rhetorical ante in their verbal exchanges recently, at a time of elevated tensions due to signs that Pyongyang may be preparing to conduct a nuclear test.

As well as repeated sexist swipes at President Park, Pyongyang's state media recently put out a racist diatribe aimed at US President Barack Obama.

Kim's remarks were triggered by what he called Pyongyang's "absurd" denials that it had anything to do with three crashed surveillance drones recently recovered on the South Korean side of the border.

Seoul said a joint investigation with US analysts had provided "smoking gun" evidence that the drones came from the North and were pre-programmed to fly over military installations in the South.