De Klerk said he wasn't aware Mandela said he "never renounced apartheid."
"I have made the most profound apology in front of the Truth Commission and on other occasions about the injustices which were wrought by apartheid," he said, referring to the panel established to help uncover past government errors and abuses and to foster amity.
He said he hasn't issued an apology for "the original concept of seeking to bring justice to all South Africans through the concept of nation states," the creation of separate black and white states.
"In South Africa it failed," he said. "And by the end of the '70's, we had to realize, and accept and admit to ourselves that it had failed. And that is when fundamental reform started."
He was then asked if apartheid failed because it was unworkable, or because it was simply morally repugnant.
"There are three reasons it failed," he said. "It failed because the whites wanted to keep too much land for themselves. It failed because we (whites and blacks) became economically integrated, and it failed because the majority of blacks said that is not how we want our rights."
Still, de Klerk would not back off his belief in the validity of the original concept of "separate but equal" nation states.
"I don't apologize for saying that what drove me as a young man, before I decided we need to embrace a new vision, was a quest to bring justice for black South Africans in a way which would not -- that's what I believed then -- destroy the justice to which my people were entitled. My people, whose self-determination (was) taken away by colonial power in the Anglo World War."
That, de Klerk said, is how he was raised.
"And it was in an era when also in America and elsewhere, and across the continent of Africa, there was still not this realization that we are trampling upon the human rights of people. So I'm a convert."