The ailing 94-year-old former South African president Nelson Mandela remains in a serious but stable condition in hospital, the Presidency announced on Saturday.

The announcement came as Mandela is spending his 14th day for receiving the treatment following he was admitted to hospital in the administrative capital of Pretoria with the serious lung infection on June 8.

"We thank the public for support and for respecting the privacy of the former president and his family," said the Presidency in a statement.

The Presidency confirmed the media report that the military ambulance transporting Mandela had an engine failure on June 8 en route from his residence in Johannesburg to Pretoria but it was soon replaced by the other military ambulance.

"The doctors were satisfied that Mandela suffered no harm during this period," said the statement.

"We appeal again that his privacy be respected and that he be accorded the doctor-patient confidentiality that all patients are entitled to in terms of medical ethics," the Presidency said.

This is the third time for Mandela to be admitted to hospital this year. On March 27, he was hospitalized after doctors diagnosed him of having pneumonia.

He was also admitted in December for recurring lung infection.