PRETORIA (AFP) - US President Barack Obama will not visit his political hero Nelson Mandela in hospital, out of deference for the anti-apartheid icon's "peace and comfort," a US official said Saturday.

Mr Obama and his wife Michelle will however spend time with Mr Mandela's family to offer "thoughts and prayers at this difficult time," the official said, as the US leader arrived in Pretoria for talks with President Jacob Zuma.

Mr Obama is in South Africa on the second stop of a three-nation Africa tour. His visit had triggered intense speculation that the United States' first African-American president might visit 94-year-old Mr Mandela in the Pretoria hospital where he has spent three weeks being treated for a lung infection.

"Out of deference to Nelson Mandela's peace and comfort and the family's wishes, they will not be visiting the hospital," the White House said in a statement. The Obamas would meet privately with members of the Mandela family "to offer their thoughts and prayers at this difficult time," the statement added.

Since starting his Africa tour in Senegal on Thursday, Mr Obama has paid fulsome tribute to the man globally admired as a symbol of struggle against injustice and of racial reconciliation for the way he led South Africa out of centuries of white-minority rule.

The U.S. president has called Mandela a "personal hero" and is due to make a tour on Sunday of Robben Island, the former penal colony where South Africa's first black president passed 18 of the 27 years he spent in apartheid jails. Mr Obama held bilateral talks on Saturday in Pretoria with South African President Jacob Zuma.