Sports minister claims he is victim of smear campaign and leaders at war as party unveils plans to mark 100th birthday

A government minister, a front-page sex scandal and claims of a honey trap set by "spooks" determined to crush enemies of the president: just another week in the turbulentlife of the African National Congress.

Africa's oldest liberation movement has unveiled plans to mark its centenary in January 2012. But where party leaders are readying for an expensive celebration, others say it will be more of a wake.

The latest episode in the party's gradual implosion involves the sports minister, Fikile Mbalula, whose extramarital liaison with a model who claims she fell pregnant by him has dominated Sunday newspapers for two weeks. The minister issued a public apology for his "acts and omissions" but denied he had undermined his government's safe sex message, aimed at combating the world's biggest HIV caseload. Leaving little to the imagination, he told South Africa's Sunday World: "The truth is that I used a condom with her, but it burst during sex."

Then on Tuesday, the New Age newspaper carried an interview with Mbalula which quoted him as claiming he was the victim of a politically motivated conspiracy orchestrated by the country's intelligence agencies.

Mbalula allegedly said that the woman was paid R150,000 (£11,842) by rogue state security operatives to destroy his reputation before ANC internal elections. The state security agency has denied the claim, and on Tuesday the ANC said Mbalula disputed the accuracy of the interview.

Mbalula's spokesman, Paena Galane, said: "We have never blamed the state security or national intelligence agencies." But asked if their involvement could be discounted, he added: "If those things exist, time will tell."

He added: "There is a cordial engagement between ourselves and the New Age. We have agreed they will give us space tomorrow to clairfy the issues that have been raised."

The tale has prompted soul-searching in South Africa about the extent to which politicians' private lives are in the public interest. But it also underlined how almost every incident is seen through the prism of a low-level civil war in the ANC.

President Jacob Zuma – who survived his own sex scandal when he was cleared of rape but then said he showered to avoid infection after sex with an HIV-positive woman – has the considerable advantage of incumbency going into the party's elective conference next year.

But ranged against him is the ANC youth league, which, though its real influence is debated, has consistently set the country's media agenda. The youth league president, Julius Malema,, who helped Zuma get elected, is said to be pushing for deputy president Kgalema Motlanthe to oust him, and for Mbalula to supplant ANC secretary general Gwede Mantashe.

When the youth league organised a recent "economic freedom" march of several thousand people in Johannesburg and Pretoria, Malema praised "great ANC presidents" Nelson Mandela and Thabo Mbeki, and Motlanthe. There was no mention of Zuma.

Malema faces his own Waterloo this week when the ANC's disciplinary committee returns its verdict on charges, instigated by Zuma, that he brought the party into disrepute with a string of offences, including a call for regime change in neighbouring Botswana. It is widely speculated that if the charismatic Malema is acquitted, Zuma will be fatally wounded.

The president's camp is evidently confident. Zuma's spokesman Mac Maharaj said: "Malema is finished. No question. He has clearly got immense leadership qualities but he has occupied a space where he has accepted a paradigm of post-independence countries: that it's politics as normal and it's only about power. He is cut adrift from the real substance of our society and challenges and the need for framing questions so you can take control of your destiny."

Either way, it is feared that internecine conflict is paralysing the party that has dominated South Africa since the dawn of democracy 17 years ago. Mbalula described "the political environment" within the ANC as "really a poisoned one" and warned his foes: "My message is that if you live a political life and start to play the game of dirty tricks, you will not survive."

Writing in the Times of South Africa, political commentator Justice Malala said: "The ANC turns 100 in January. It will celebrate more divided, more corrupt, more battle-bruised, more rudderless than it has ever been in its history."