In response to the historic handshake between Barack Obama and Cuban president Raul Castro, the US National Security Council has said: "This wasn't a pre-planned encounter. Above all else, today is about honouring Nelson Mandela and that was the President's singular focus at the memorial service.
"We appreciate that people from all over the world are participating in this ceremony."
Pictures released today give a unique look inside Air Force One as two former and one current US President flew to Nelson Mandela's memorial
Twenty years ago the soon to be President Mandela pledged to 'wash away the stains of apartheid' - two decades on those stains remain.
Barack Obama has led the tributes to Nelson Mandela saying that South Africa's democracy is his 'cherished legacy.'