SEOUL (AFP) - North Korea on Wednesday slammed the South after activists sent anti-Pyongyang leaflets over the border in balloons, warning that such launches have scuppered high-level talks in the past.

The isolated nation cautioned Seoul that the "reckless act" of leaflet scattering by North Korean defectors - who it called "human scum" - could threaten the tentative dialogue, state-run Korean Central News Agency (KCNA) said.

"On January 5, human scum... of an organisation of 'defectors from the north' organised the scattering of over 1.3 million leaflets slandering the dignity and social system of the DPRK (Democratic People's Republic of Korea)," KCNA said.

"It is... a last ditch effort to obstruct the improvement of north-south relations and spoil an atmosphere of dialogue," it said, calling on the South to "clarify" its stand.

In October last year, balloons sent from the South sparked a brief exchange of heavy machine-gun fire across the border when the North attempted to shoot them down.

The incident scuppered a planned resumption of high-level talks between the two Koreas.

South Korean President Park Geun Hye on Tuesday welcomed North Korean leader Kim Jong Un's New Year statement that he was open to the highest-level talks.

Mr Kim said the North would seek talks on the condition that the South ceased its annual joint military exercises with the United States and stopped criticising his regime.

But just days after Mr Kim's statement, South Korean activists on Monday launched balloons across the border carrying leaflets condemning the Pyongyang regime.

"The South Korean authorities should not forget the fact that last year the atmosphere of dialogue... was spoiled due to the human scum's leaflet scattering," KCNA said in the statement on Wednesday.

North Korea also accused the US of funding activists to carry out the leaflet drop.

The prospects for any meaningful dialogue are still unclear.

South Korea has made it clear that it will not stop its annual military exercises with the US - such as the Key Resolve/Foal Eagle drill expected to start in late February - which it says are purely defensive.

South Korea's unification ministry, which handles cross-border affairs, on Tuesday reaffirmed the South's position that there is no legal basis for a blanket ban on leaflet launches.