President Obama, in the midst of an historic tour of Africa, says he's not sure whether he'll be able to visit gravely ill Nelson Mandela when he arrives in South Africa today.

Speaking to reporters aboard Air Force One en route from Dakar, Senegal to Johannesburg, Obama said, "We'll see what the situation is when we land."

Obama adds, quote, "I don't need a photo op and the last thing I want to do is to be in any way obtrusive at a time when the family is concerned with Nelson Mandela's condition."

Obama said, "I think the main message we'll want to deliver, if not directly to him, but to his family, is simply profound gratitude for his leadership." Mandela is a former president of South Africa.