South African officials have confirmed that the ambulance which took former South African president Nelson Mandela to hospital two weeks ago broke down.
US network CBS reported that Mr Mandela had to wait by the side of the road for 40 minutes.
The incident happened at night in freezing temperatures before he was transferred to another ambulance.
A South African government spokesman said there was no threat to Mr Mandela's health from the incident as he was tended to by intensive care nurses throughout.
Mr Mandela, 94, is being treated for a recurrence of a lung infection.
He remains in a "serious but stable" condition in hospital.
The 94-year-old anti-apartheid leader's health has not changed since his admission to a Pretoria hospital two weeks ago.
Mr Mandela, who became South Africa's first black president in 1994, was rushed to a Pretoria hospital early on 8 June with a recurring respiratory infection.
A presidential spokesman said the former president was transferred to another military ambulance for the remainder of the almost 50-minute journey between Johannesburg and the Medi-Clinic Heart Hospital in Pretoria.
Doctors attending to Madiba, the clan name by which Mr Mandela is popularly known, were satisfied that he suffered no harm during this period, he said.
Failure to deliver basic services under the African National Congress-led government has sparked violent protests across the country this year.
These factors are being used as campaign points for political parties jostling for position ahead of next year's election.
Mr Mandela's history of lung problems dates back to his time at Robben Island prison near Cape Town.
He was released in 1990 after 27 years and went on to serve as president from 1994 to 1999.
His hospitalisation is the fourth since December.