People continue to pay tribute to Mandela outside the Pretoria hospital where he is being treated. Mandela, who turns 95 on Thursday, is recovering from a recurring lung infection and has been in the hospital for more than five weeks.
Friends who have visited him say he is on life support in the form of mechanical ventilation. The most recent official update on his health said Mandela was in critical but stable condition. Both Mandela's wife, Graca Machel, and President Jacob Zuma have said Mandela is responding to treatment.
Mandela spent 27 years in prison, and then went on to become South Africa's first black president in 1994. Mbeki was Mandela's key deputy and succeeded him as South Africa's president in 1999.
The Associated Press contributed to this report.