The ANC's powerful 107-member national executive committee (NEC) met for 13 hours at a hotel outside Pretoria, and decided it would "recall" Zuma from his job as national president, several local independent media said.
Mmusi Maimane, the leader of the main opposition Democratic Alliance party called the recall an "internal ANC resolution, nothing more". "The NEC themselves said that I must resign‚ and I find that very unusual that I should do so because this is not the first time that they've said this‚" President Zuma said.
Nevertheless, he said it is "generally thought in South Africa that the NEC want to get rid of Jacob Zuma".
Zuma said he would make another statement later Wednesday, raising the possibility that he might change his position and resign voluntarily rather than face the humiliation of his ouster by the combined votes of the ruling and opposition parties.
The ANC's former head of intelligence, Zuma, 75, took office in May 2009, just weeks after prosecutors dropped graft charges against him. He has resisted increasing pressure to quit since December, when Cyril Ramaphosa replaced him as leader of the ANC.
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However, he would then be expected to face a confidence vote in Parliament. "He hasn't been told yet", said the senior ANC source on Tuesday.
The stalemate over his departure has left Africa's most developed economy in limbo, with a series of public events cancelled last week, including Thursday's State of the Nation address to Parliament. If Zuma digs in and refuses to be fired, he has to be removed through a parliamentary motion.
The President's term had been due to end next year.
"We haven't given him any deadline to respond (but) when we recall our (president), we expect (him) to do what the organization expects him to do".
A year ago the Supreme Court of Appeal ruled that he must face 18 counts of corruption, fraud, racketeering and money laundering relating to a 1999 arms deal. Late past year, South Africa's top court ruled that he violated the constitution when he paid for multimillion-dollar upgrades to his private home with state funds.
And Zuma's close ties to the Guptas have been blamed for their rise.