US President Barack Obama has visited Nelson Mandela’s Robben Island prison cell during the Cape Town leg of a three-day trip to South Africa. Obama’s visit has been overshadowed by the health of the anti-apartheid hero.

Obama paid tribute to South Africa's first black president, Nelson Mandela, by taking his family on a tour of the island prison where the ailing anti-apartheid leader spent 18 of his 27 years imprisoned.  

The Obama family visited Mandela's Robben Island prison cell as well as the lime quarry where Mandela was forced to work during his incarceration and where the lung problems afflicting him today first developed. 

The Obamas' tour guide, 83-year-old politician Ahmed Kathrada, who had been detained in the prison for two decades, told the family of his experiences of being forced to work every day.

Prior to the visit, Obama had said he was paying tribute to a man who inspired his political activism.

"The struggle here against apartheid, for freedom, Madiba's moral courage, his country's historic transition to a free and democratic nation, has been a personal inspiration to me," said Obama using Mandela's clan name.

It was a privilege, he added, to be able to show his children the place where Mandela spent many years as a political prisoner. "For me to be able to bring my daughters there and teach them the history of that place and this country…that's a great privilege and a great honor," Obama added.

Mandela, a Nobel Peace Prize winner, is critically ill with a recurrent lung disease in a Pretoria hospital, where he was admitted three weeks ago.

Obama and First Lady Michelle met privately late Saturday with Mandela's relatives. A White House statement said Obama would not be meeting the critically ill anti-apartheid leader in hospital.

"Out of deference to Nelson Mandela's peace and comfort and the family's wishes, they will not be visiting the hospital," the unnamed official told the news agency AFP.

Signature speech

Later on Sunday, Obama is set to deliver what the White House called the signature speech of his weeklong trip to the continent at the University of Cape Town.

During the speech, Obama will announce plans to unveil a 7-billion-euro ($9.1 billion) initiative to upgrade African electricity networks, in an attempt to end power outages that deter business investment.

Meanwhile, Obama is set to host a landmark meeting of sub-Saharan Africa leaders next year, the White House announced on Sunday.

The announcements comes as Obama dismisses talk of a tussle with China for influence on the continent.

On Saturday, Obama met with South African President Jacob Zuma in Pretoria. The two leaders held talks focusing on trade, boosting economic ties and regional security in Africa.

Obama's three-country tour concludes next week in Tanzania.

jlw/kms (AFP, dpa, AP)