Nelson Mandela remains in a critical condition in hospital, South Africa's President Jacob Zuma said.
Mr Zuma and ANC deputy president Cyril Ramaphosa visited Mr Mandela in hospital on Sunday evening after the former president's health deteriorated.
They were briefed by Mr Mandela's medical team and told the 94-year-old's condition had become critical over the past 24 hours".
Mr Zuma said in a statement: "The doctors are doing everything possible to get his condition to improve and are ensuring that Madiba is well-looked after and is comfortable. He is in good hands."
The pair also met Mr Mandela's wife, Graca Machel, who has been by her husband's bedside since he was taken ill.
On Monday, Mr Zuma told a news conference in Johannesburg that he had no further updates on Mr Mandela's condition.
Mr Mandela has suffered repeated bouts of illness in recent months and has been admitted to hospital four times since December.
The anti-apartheid leader has been in intensive care since he was last admitted to hospital on June 8 for a recurring lung infection.
Mr Zuma appealed to South Africans and to the world to pray for Mr Mandela, his family and the medical team attending him.
In Sunday's statement, Mr Zuma also discussed the government's acknowledgement a day earlier that an ambulance carrying Mr Mandela to the hospital two weeks ago had broken down.
"There were seven doctors in the convoy who were in full control of the situation throughout the period. He had expert medical care," Mr Zuma said.
"The fully equipped military ICU ambulance had a full complement of specialist medical staff including intensive care specialists and ICU nurses.
"The doctors also dismissed the media reports that Madiba suffered cardiac arrest. There is no truth at all in that report."
Mr Mandela is seen by many around the world as a symbol of reconciliation.
He played a leading role in steering South Africa from the apartheid era to democracy, becoming the country's first black president in all-race elections in 1994.