Nelson Mandela remained in hospital on Sunday after keyhole surgery that officials said had left him in no danger but increased South Africans' concerns for their aging former president.

President Jacob Zuma told the country not to panic after the 93-year-old anti-apartheid leader was hospitalised with chronic abdominal pain on Saturday, saying he should be discharged on Sunday or Monday.

In the latest health update, Defence Minister Lindiwe Sisulu said Mandela had had investigative laparoscopy - where a tiny camera is inserted into the abdomen - and denied reports that he had undergone surgery for a hernia.

It wasn't the surgery that has been out there in the media at all, Sisulu told a media briefing in Cape Town. He's fine. He's as fine as can be at his age - and handsome.

The government has not revealed where Mandela is being treated, although reporters were being kept at a distance from Pretoria's 1 Military hospital, which is officially responsible for the health of sitting and former presidents.

Zuma said in a statement late on Saturday that Mandela, who is popularly known by his clan name, Madiba, was fine and doctors were satisfied with his condition.

He was in good health before admission in hospital but doctors felt the complaint needed a thorough investigation, he said. We are happy that he is not in any danger and thank the doctors for their hard work and professionalism.

Mandela has been in poor health since he was hospitalised a year ago with respiratory problems, and has not appeared in public since.

His admission on Saturday renewed fears for the health of South Africa's first black president, who still occupies a central position in the psyche of a country ruled by the 10 percent white minority until all-race elections in 1994.

Despite widespread public affection, most accept that Mandela, who was incarcerated for 27 years by the apartheid government, may not live for much longer.

We wish him well, said Soweto resident Ronny Zondi. But understanding his age, we've got to accept he might not be with us for long. We wish that God could keep him longer.

Mandela's last public appearance was in July 2010 at the final of the World Cup in Johannesburg's Soccer City stadium. He now divides his time between his home in Johannesburg's northern suburbs and his ancestral village of Qunu in the Eastern Cape.

The government's public comments on Mandela's hospitalisation have been markedly more open than a year ago.

Then, Zuma's office took hours to confirm media reports of a sudden decline in Mandela's health, leading to a scrum of local and international reporters outside Johannesburg's Milpark hospital.

(Reporting by Ed Cropley; Editing by Robin Pomeroy)