US President Barack Obama is to meet members of Nelson Mandela's family during his visit to South Africa, the White House says.

But officials confirmed that the president will not see the ailing leader himself, who is in a critical conditions in hospital.

Obama's Air Force One landed in Pretoria on Friday, June 28 evening, as part of his three-country tour of Africa. He is holding talks with his South African counterpart, Jacob Zuma.

The US president has described Mandela as a "hero for the world".

Mandela, who is 94, is critically ill in hospital, where he was admitted on 8 June with a recurring lung infection.

His ex-wife, Winnie Madikizela-Mandela, said on Friday she felt it would not be right for President Obama to visit him while he was in a critical condition.

"I'm not a doctor but I can say that from what he was a few days ago there is great improvement, but clinically he is still unwell," she said.