His admission comes less than three months after being treated for a lung infection and gallstones.

“There isn’t an update. I just have to allow the doctors to advise me,” said presidential spokesman Mac Maharaj.

One of Mandela’s grand-nephews insisted that the former statesman was simply undergoing tests.

“It’s a normal check up at the hospital as an old person,” he told AFP.

Maharaj could not say how long the former statesman would have to stay at the facility this time, after an 18-day hospitalisation in December.

“It all depends on the doctors,” Maharaj told AFP.

The presidency said Mandela, 94, was hospitalised Saturday for checkups “to manage the existing conditions in line with his age”.

They did not divulge at which Pretoria hospital he was staying.

But a witness told AFP that patients at the Mediclinic Heart Hospital were on Saturday moved out of the ward that Mandela stayed in during his December hospitalisation.

The hospital told them the ward needed to be repainted, but no one was allowed near the area.

The country’s ruling ANC said he was “in capable and competent hands,” said spokesman Jackson Mthembu in a statement.

The party echoed the presidency’s words “that this is a routine check-up and therefore should not raise alarm.”

“The African National Congress wishes Madiba well,” said Mthembu, using the clan name which the icon is affectionately known by.

Mandela underwent treatment for a recurrent lung infection and surgery to extract gallstones over Christmas, during his longest stint in hospital since his release from prison in 1990.

He was discharged the day after Christmas and was last known to be convalescing at his home in Johannesburg.

President Jacob Zuma’s office said in January he had “recovered” from the infection and surgery.

A month later Zuma found Mandela “comfortable and relaxed” and watching television, during a visit at his house.

The revered statesman has not appeared in public since South Africas Football World Cup final in 2010, six years after retiring.

Rumours of his failing health or even death flare up periodically, forcing the government to issue assurances that all is well.

But the presidency — the only authority to speak on his health — has been known to play down his treatments as routine checkups.

His December hospitalisation was attributed to tests “consistent with his age”.

In January 2011 his two-night hospitalisation for an unnamed acute respiratory infection was also initially described as “routine” testing.

Mandela the man has grown increasingly frail in recent years, with health complications often linked to years of hard labour in prison for opposing apartheid.

In February last year he spent a night in a medical facility for a minor exploratory procedure to investigate persistent abdominal pain.

While serving his 27-year prison term, Mandela was diagnosed with early stage tuberculosis in 1988, a disease which killed his father.

In 2001, he received radiotherapy treatment for prostate cancer and said the following year he had been given a clean bill of health against the disease.

South Africa’s first black president served one term after winning historic all-race elections in 1994.

He is revered as the symbol of the country’s peaceful shift into democracy after decades of racist white minority rule.

In recent years he has stayed out of the public eye at his rural home village Qunu in the Eastern Cape.

The last confirmed image of the statesman was a picture taken with then-US secretary of state Hillary Clinton, when she visited him last August.

At the beginning of February two of his granddaughters released a picture of a smiling Mandela sitting with his youngest great-grandson in an arm-chair.

It was taken to show his recovery after his December hospitalisation, they said while promoting their new reality show, Being Mandela.