North Korea threatened Thursday to disclose a voice recording of a secret meeting with South Korea, at which it says Seoul "begged" for summit talks.

The North last week disclosed the May meeting in Beijing and says the South proposed holding a series of three summits to ease months of high tensions. It rejected the offer.

The South admitted holding such a meeting but said its neighbour was misrepresenting its purpose, a claim denied Thursday by the North's powerful National Defence Commission (NDC).

The NDC described the South's account of the Beijing talks as a "sheer lie" and said it would disclose a recording of the entire conversation if Seoul refused to speak the truth.

"The (South Korean President) Lee Myung-Bak group of traitors would be well advised to make a clean breast of the contact before it becomes too late," it said.

Pyongyang in the past fortnight has made a series of verbal attacks and threats against Seoul's conservative government, vowing to have no more dealings with it.

Last Friday its military threatened retaliation unless Seoul punishes troops who used pictures of Pyongyang's ruling dynasty as rifle-range targets.

The South said the practice was not officially approved and had now been banned.

The two sides have given different accounts of the Beijing meeting. The North said the South begged for summit talks and even tried to bribe its delegates.

The South denied any bribery bid and said the key purpose of the talks was to get the North to apologise for two deadly border incidents last year and to promise no recurrence.

On Thursday the South's unification ministry denounced Pyongyang for trying to shift responsibility for strained ties to Seoul and also to split public opinion in the South.

"North Korea is expected to take a quite firm attitude for a while," it said, attributing Pyongyang's hardline stance to a race among North Korean officials to demonstrate loyalty to their leader.

The South last year imposed trade sanctions after accusing the North of sinking one of its warships in March 2010 with the loss of 46 lives.

The North denies involvement in the sinking. But it shelled a South Korean border island last November, killing four people including two civilians.

It says the shelling was provoked by its neighbour and refuses to apologise for either incident.