The denunciations in state media said "reptile media" were making allegations designed to "hurt the dignity" of Mr Kim, his wife, Ri Sol-ju, and the regime.
The state-run KCNA news agency claimed the reports were the work of "psychopaths" and "confrontation maniacs" in South Korea's government and the media.
"This is an unpardonable, hideous provocation hurting the dignity of the supreme leadership," KCNA stated. "Those who commit such a hideous crime ... will have to pay a very high price."
Reports in South Korea initially claimed that Hyon Song-wol, with whom Mr Kim was romantically linked around 10 years ago, was among a dozen well-known North Korean singers and musicians executed by firing squad on August 20 after appearing in pornographic videos.
Relatives of the condemned musicians and other members of the Unhasu Orchestra, the Wangjaesan Light Band and the Moranbong Band were forced to watch the executions before being sent to labour camps. » | Julian Ryall, Tokyo | Monday, September 23, 2013