South African Deputy President Cyril Ramaphosa called Sunday for an independent probe into suspected corruption in the upper echelons of power.
"We must be honest and brave enough to confront state capture," he said, using a term referring to allegations of corruption by President Jacob Zuma and his associates.
Tens of thousands of South Africans have staged protests in recent weeks demanding Zuma stand down, and opposition parties, religious groups and civil society activists last week joined forces in a new alliance against him.
"Unless the ANC addresses these challenges, we can be certain that our electoral support will continue to slide," Ramaphosa warned.
"I support that there should be a judicial commission of inquiry. And we must be prepared to talk about these things openly and honestly, as our forebears did," he said in a speech paying tribute to anti-apartheid icon Chris Hani who was assassinated in 1993.
Zuma's sacking of respected finance minister Pravin Gordhan last month fanned public anger over government graft scandals, record unemployment and slowing economic growth.
In his speech, Ramaphosa referred to recommendations by the former head of South Africa's anti-corruption watchdog Thuli Madonsela, who last year issued a damning report calling for a judicial inquiry into Zuma's relationship with a wealthy business family.
Zuma has been accused of being in the sway of the Gupta family, allegedly granting them influence over government appointments, contracts and state-owned businesses.
The Constitutional Court also last year found Zuma guilty of violating the constitution after he refused to repay taxpayers' money used to refurbish his private rural house.
The African National Congress (ANC) has been in power since the end of apartheid in 1994 but has lost popularity in recent years and won only 54 percent of the vote in 2016 local elections, its worst ever performance.
Zuma, who came to office in 2009, is due to step down as head of the ANC in December, and as national president ahead of the 2019 general election.
Ramaphosa, who was highly critical of the sacking of Gordhan, is one of the favourites to become party leader along with Nkosazana Dlamini-Zuma, the ex-wife of the current president and the former head of the African Union Commission.