US President Barack Obama met Saturday with family members of ailing South African statesman Nelson Mandela and spoke by telephone with Mandela's wife as she maintains a vigil by his bedside.

However, he and first lady Michelle Obama will not visit the anti-apartheid icon at the hospital "out of deference to Nelson Mandela's peace and comfort, and the family's wishes," the White House said, as cited by CNN.

"I expressed my hope that Madiba draws peace and comfort from the time that he is spending with loved ones, and also expressed my heartfelt support for the entire family as they work through this difficult time," Obama said after meeting with Mandela family members in Johannesburg.

Madiba is Mandela's clan name.

Those present for the meeting at the Nelson Mandela Foundation included Mandela's two daughters, Makaziwe and Zindzi, and eight of his grandchildren.

"I have drawn strength from the support received from President Barack Obama, Michelle, Malia and Sasha," said Mandela's wife, Graca Machel, of her phone conversation with the US president.

Machel said she had already conveyed the Obama family's "messages of strength and inspiration" to her husband.

Obama earlier held bilateral talks with South African President Jacob Zuma in Pretoria, with trade high on the agenda.

In a news conference after the talks, both paid tribute to Mandela's contributions as an anti-apartheid campaigner and former president.

"I know that he is your personal hero as well," Zuma said. "The two of you are also bound by history as the first black presidents of your respective countries. Thus, you both carry the dreams of millions of people in Africa and in the diaspora who were previously oppressed."