"This is a serious accusation that casts aspersions on the integrity of the presidency," spokesperson for the presidency Harold Maloka said on Tuesday.
The presidency took exception to Jansen saying its official descriptions of Mandela's hospital visits as routine check-ups were inaccurate, he said in a statement.
"Professor Jansen should prove his allegation or retract." The presidency was responding to an article in the Volksblad newspaper on Monday.
According to the report, Jansen said presidential spokesperson Mac Maharaj was lying when he said Mandela went to hospital for check-ups.
"When you are 94, you go to hospital to die; not for routine tests," Jansen was quoted as saying. He also reportedly said he wished Mandela would die.
According to the Volksblad article, Jansen reportedly asked a group of about 250 students: "Don't you also wish he would die?"
Volksblad reported that the students were noticeably shocked when they heard the question. However, on Monday afternoon Jansen dismissed the report and said it was a misrepresentation.
"My argument was that Madiba had done so much for South Africa, that he had served South Africa well, and that sometimes you just wish that people would leave him alone so that he can pass his final days quietly."
Jansen said he wanted Mandela to live as long as possible, but without the constant glare and speculation.
"He needs to be left alone to rest and die in peace. That was the content and context of what I said.
"To misrepresent a lengthy statement on a talk which was entirely devoted to extolling Madiba's leadership – alongside that of [Albert] Luthuli, [Mahatma] Gandhi, and Martin Luther King, Jr – is mischievous."
Jansen said the seven characteristics of leadership of Mandela, and the other three leaders, were what the hour and 10 minute talk was about.
This was something completely ignored in the misrepresentation. Jansen said he did argue the official representation of the hospital visits as "routine check-ups" was inaccurate for aged people, since at the age of 94, no hospital visit was routine.
"That is what I said." Mandela was discharged on Saturday, after being admitted to a Pretoria hospital on March 27 to receive treatment for a lung condition. – Sapa