The controversial letter by Winnie Madikizela-Mandela, in which she repeats rumours about President Thabo Mbeki's personal liaisons with five women, including three ministers or deputy ministers, stems from a broader struggle within the ANC, according to well-placed sources.
In the letter, Mandela complains about an attack launched on her by the president at an ANC national working committee meeting in Durban in May. She says the president falsely accused her of spreading rumours that he had taken out a leading Gauteng politician's wife one evening "and brought her back at 5 am".
She also repeats rumours she says were circulating at ANC headquarters about Mbeki and four other women, three of them members of his cabinet.
The letter, which was leaked last week, was written by Madikizela-Mandela to Deputy President Jacob Zuma months ago. ANC insiders said it was no coincidence that it was leaked on the eve of Mbeki's New Year ANC address and just before a crucial ANC meeting that took place in Johannesburg this week.
The sources point to two camps, which have developed in the ANC, one around the president and the other, including Mandela, loosely associated with Zuma.
"The ANC is a family that is not at peace with itself. That is the background to this letter," said one source.
Two independent sources alleged that Zuma and Mbeki had been barely on speaking terms for some time. They said Zuma had been unhappy with the way Mbeki had treated him since he became deputy-president in 1999.
Rumours circulated prior to this week's ANC lekgotla (bosberaad) that there might be a move afoot to get Mbeki to step down as ANC president while retaining his position as national president.
Both Zuma's name and that of Government Communication and Information Service head Joel Netshitenzhe were mentioned, but it was considered unlikely that any such moves would emerge at this stage.
The lekgotla has been taking place under tight security with access to cellphones restricted.
The struggle over the nature and direction of any probe into irregularities in South Africa's R43 billion arms procurement deal has apparently also been taking place against the backdrop of tensions within the ANC.
It was Zuma who intervened to counter Mbeki confidante Essop Pahad during internal ANC debate over the probe.
Later, in responding to leaks about the confidential arms probe discussion, Pahad warned the media against being used by groups to settle internal party disputes.
Attempts to get comment from the President's office or from Mbeki via the ANC were all unsuccessful.