The EFF has rejected the FW de Klerk Foundation's apology regarding its statement on apartheid not being a crime against humanity.
The party wanted De Klerk to be stripped of his Nobel Peace Prize and any privileges he got as a former head of state. The EFF also called for him to face the might of the law.
"As the EFF, we reject the apology as one that lacks sincerity and relevance, as the individual who was the source of these hateful views remains unrepentant and avoids accountability by using a foundation which bears his name," the opposition party stated on Monday.
"We believe that the time for empty apologies in South Africa as a means of reconciliation is over. Apologies for the brutality black South Africans have experienced has taken various forms in South Africa, with all of them being publicity stunts.
"There must be a decisive move from efforts of reconciliation to justice, as justice is the only form of recourse that can be taken against those who refuse to repent for the evils they have committed."
This is the latest development following the EFF's call for the removal of De Klerk from Parliament ahead of President Cyril Ramaphosa's State of the Nation Address (SONA) on Thursday.
De Klerk was a guest at SONA in his capacity as a former deputy president in the Government of National Unity formed after the first democratic election of 1994.
He and his wife, Elita, were in the public gallery with former presidents Thabo Mbeki and Kgalema Motlanthe.
Former president Jacob Zuma was not present and is understood to be receiving medical treatment.
Since Thursday, Mbeki was quoted as saying that De Klerk told him he was not aware that the United Nations had declared apartheid a crime against humanity.
The foundation in De Klerk's name issued a statement saying De Klerk and his wife had been subjected to "vitriol" by the EFF, and explained that De Klerk had apologised and dedicated his presidency to the abolition of apartheid.
It added the question: "But was apartheid a crime against humanity?" and claimed that the UN's Convention on the Suppression and Punishment of the Crime of Apartheid was driven by Russian propaganda. It also questioned the credibility of some of the signatories and attempted to compare the number of people killed by apartheid security forces to that of other conflicts.
Anglican Archbishop Emeritus Desmond Tutu was among those who weighed in, slamming debate over the degree of how bad apartheid was.
The FW de Klerk Foundation has since retracted the statement, but a protest march is nevertheless planned for Wednesday to its offices in Cape Town.
The EFF's position is that De Klerk be subjected to a forensic inquiry on his role during apartheid, that he be stripped of the Nobel Peace Prize awarded to him and that he also lose his privileges as a former head of state.
"That he lied to former president Thabo Mbeki and faked ignorance of the UN declaration on apartheid is a sign of mockery by a man who has justified his views and refuses to accept his role in the deepening of colonialism and anti-black racism in this country," said the EFF.
The Luthuli Peace and Development Institute, set up in the names of another Nobel Peace Prize recipient Albert Luthuli and his wife, Nokukhanya, also rejected De Klerk's apology as "a mere exercise in public relations management" and called his denial of apartheid as a human rights violation "crass".
"We believe that to deny apartheid as a crime against humanity, is to trample on the lived experiences of the millions of apartheid's victims," the foundation said.
"Such false narratives about the true history of South Africa leads to the miseducation of young South Africans of all races and disempowers humanity from ensuring that no such scourge is visited upon any people in any country of the world now and in the future. We urge all South Africans to work at destroying the deep wounds that resulted from apartheid."
- Compiled by Jenni Evans