"If we look at the statement released by the Presidency -- it does not state that Mandela is going in for surgery. We do not want any speculation," African National Congress spokesman Keith Khoza said.
"His [Mandela's] admittance was pre-arranged. Mandela was complaining about abdominal pain -- now it is a matter that his doctors and specialists will decide on."
Khoza was commenting after the British Broadcasting Corporation (BBC) reported that Mandela was "stable" after undergoing surgery.
Mandela's oldest granddaughter said she was not worried about his hospitalisation as the 93-year-old had been "in perfect health" earlier this week.
"I don't see it as a big thing. He's in perfect health. When I saw him on Wednesday, he was in good spirits, in perfect health, and, you know, the epitome of health really for a man of his age," Ndileka Mandela told AFP.
"I'm not worried. I mean grandad rebounded from his illness last year. I don't see any reason why this should be any different."
Earlier on Saturday, Presidency spokesman Mac Maharaj said he was still waiting for an update on Mandela's health.
"We want to give the specialists time to attend to him first and then they will provide us with a full report that will be presented to President Jacob Zuma," said Maharaj.
"Before he was admitted this morning [Saturday] he was doing well. We have an obligation to the public to keep them informed on Mandela's health and will do so -- when we have news."
"We want to handle the matter with due regard to his privacy. We will give you updates as soon as we have any," he said.
Both the Presidency and the ANC wished him a speedy recovery.
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