Former South African President Nelson Mandela remains in a critical condition in hospital, President Jacob Zuma says.
Mr Zuma said the doctors were doing everything they could to make the former leader comfortable, but he could not give any more medical details.
South Africa's first black president, 94, was taken to hospital in Pretoria earlier this month for the third time this year, with a lung infection.
A senior official said South Africans should not hold out "false hopes".
On Sunday, the presidency announced that Mr Mandela had become critical, after Mr Zuma visited him in hospital.
Mr Zuma said on Monday he had found Mr Mandela asleep, but had spoken to his wife and medical teams.
"All of us in the country should accept the fact that Madiba [Nelson Mandela's clan name] is now old. As he ages, his health will... trouble him and I think what we need to do as a country is to pray for him."
Mac Maharaj, Mr Zuma's spokesman, told the BBC's Newshour on Sunday said this was a stressful time for the Mandela family.
"I think there is need to be sombre about the news. There is a need not to hold out false hopes but at the same time let's keep him in our thoughts and let's will him more strength," he said.
Nelson Mandela's daughter, Makaziwe, whom he had with his first wife Evelyn, asked in an interview with CNN on Saturday for the family's privacy to be respected.
"Other people want to lecture us on how we should behave, and what we should do," she said.
"Really, it's our dad, it's the children's grandfather. We've never had him in our life for the better part of our years. This is in a sense quality and sacred time for us, and I would expect the world to really back off and leave us alone."
The ANC - the party of Mr Mandela and Mr Zuma - said it "noted with concern" the latest reports, and that it joined the president in calling "for us all to keep Madiba, his family and medical team in our thoughts and prayers during this trying time".
The BBC's Karen Allen reports from outside the Pretoria hospital that the mood in the country is sombre, and reality is sinking in.
It is not known what kind of condition precipitated the deterioration, she says.
There has been little information about his condition in recent days. On 13 June Mr Zuma said Mr Mandela's health continued to improve but that his condition remained serious.
Mr Mandela is revered for leading the fight against white minority rule in South Africa and then preaching reconciliation despite being imprisoned for 27 years. He left power after five years as president.
The former president and Nobel Peace Prize winner is believed to have suffered damage to his lungs while working in a prison quarry.
He contracted tuberculosis in the 1980s while being held in jail on the windswept Robben Island.
Mr Mandela retired from public life in 2004 and has rarely been seen at official events since.
On Saturday, it emerged that the ambulance in which Mr Mandela was taken to hospital on 8 June broke down, meaning he had to be moved to another vehicle.
But Mr Zuma said he had been assured that "all care was taken to ensure his medical condition was not compromised".
"There were seven doctors in the convoy who were in full control of the situation throughout the period. He had expert medical care," he said.
Mr Zuma also denied reports that the former leader had suffered a cardiac arrest.