JOHANNESBURG, Feb. 6 (Xinhua) -- Top officials in South Africa's ruling African National Congress (ANC) could not agree on whether President Jacob Zuma must resign, the party's deputy secretary-general said on Tuesday.

"The NWC (National Working Committee) has discussed the issue surrounding the future of President Jacob Zuma," Jessie Duarte told reporters.

Zuma's delivery of the State of the Nation Address, originally schueduled for Thursday, has been postponed, parliament speaker Baleka Mbete announced.

A new date will be announced soon, said Mbete.

"When we met the president this afternoon, we then learned that he was already writing to parliament, to ask for the postponement," he said.

Leaders of various political parties held a crisis meeting in parliament Tuesday afternoon. ANC leaders have held marathon meetings amid mounting pressure for Zuma not to deliver the State of the Nation Address.

Meanwhile, the Neslon Mandela Foundation has weighted in to urge Zuma to resign.

"We've now reached a point where South Africans can no longer wait for him to do so," the foundation said in a statement.