Mr Obama said earlier he did not expect to see former President Nelson Mandela, who is critically ill in hospital. Leaving Senegal, he told reporters on board Air Force One: "I don't need a photo op." Meanwhile, Mr Mandela's ex-wife, Winnie Madikizela-Mandela said the former leader had made "a great improvement" in recent days, but was "still unwell". But she said she felt it would not be right for the US president to visit Mr Mandela while he was in a critical condition. Correspondents say security is tight in the streets near Mediclinic Heart Hospital in the capital, Pretoria, where the 94-year old is being treated for a lung infection.