The denial came a day after the North indefinitely postponed reunions for families divided by the Korean War, citing South Korean hostility, slander and provocation.
Sunday's denunciation focused on several recent reports carried by the South's "reptile media" aimed at "hurting the dignity" of supreme leader Kim Jong-Un.
In particular it cited a Saturday report in Japan's Asahi Shimbun newspaper -- picked up by South Korean broadcasters and websites -- that several members of the North's Unhasu Orchestra and other state music troupes had been executed by firing squad for taping themselves having sex.
Ri Sol-Ju, Kim's wife, is a former member of the orchestra.
Asahi said the rare execution of state performers, including a singer rumoured to be Kim's ex-girlfriend, had been ordered to squash rumours of Ri's decadent lifestyle while she was an entertainer.
It said police had secretly recorded conversations between the entertainers who said, "Ri Sol-Ju used to play around in the same manner as we did".
The source for the Asahi report was a "high-ranking North Korean government official who recently defected".
South Korea's Chosun Ilbo newspaper had reported the alleged executions last month, but there was no response from Pyongyang at the time.
The North's state news agency KCNA said the reports were the work of "psychopaths" and "confrontation maniacs" in the South Korean government and media.
"This is an unpardonable, hideous provocation hurting the dignity of the supreme leadership," KCNA said in a commentary.
"Those who commit such a hideous crime ... will have to pay a very high price," it warned.
Kim Jong-Un's stylish wife has often been photographed accompanying him at official events -- in a break from the past when the North's first ladies were kept out of the limelight.
She was pictured wearing stylish, expensive-looking outfits and on one occasion sported what appeared to be a Christian Dior handbag, in a country plagued by chronic poverty.
Inter-Korean relations had recently showed signs of improving after months of heightened military tensions following the North's third nuclear test in February.
The most visible step forward was an agreement to open a jointly-run industrial estate that was shut down when the tensions were at their peak.
But they hit a new stumbling block when Pyongyang abruptly postponed the family reunions scheduled to begin on Wednesday.
