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."
President Raul Castro says Nelson Mandela set an "insurmountable example" to Latin America and the Caribbean which he says are "currently moving towards unity and integration for the benefits of their peoples on the basis of respect for diversity".
Cuban President Raul Castro is speaking at the memorial service for Nelson Mandela.
He described Mandela as the "ultimate symbol of dignity and unwavering dedication to the revolutionary struggle for freedom and justice".
US President Barack Obama shook hands with his Cuban counterpart Raul Castro at the memorial service . He is due to address the stadium shortly.
Watch the video of the historic handshake
Read more: Obama leads tributes to Mandela at memorial service
US President Barack Obama will lead tributes from world leaders to Nelson Mandela tomorrow at the memorial service in Johannesburg.
UN Secretary General Ban Ki-moon will lead the international tributes, followed by Dr Nkosazana Dlamini Zuma from the African Union.
Obama will be followed by Brazil's President Dilma Rousseff, China's Vice-President Li Yuanchao, Namibia's President Hifikepunye Pohamba, India's President Pranab Mukherjee and the last international tribute will come from President Raul Castro.
In a surprise move, Cuba's new parliament has named a rising young star as Raul Castro's first vice president.
Miguel Diaz-Canel, 52, a member of the political bureau who rose through the party ranks in the provinces to become the most visible possible successor to Castro.
Diaz-Canel would succeed Castro if the 81-year-old cannot serve his full term.
Cuba's President Raul Castro has announced that he will stand down from office in 2018 bringing to an end almost 60 years of rule under the family dynasty.
Raul took over from his brother Fidel Castro in 2008, but has spoken about limiting the number of terms for senior government officials including the presidency.
Castro made the announcement in a nationally broadcast speech shortly after the Cuban National Assembly elected him to a second five-year term in the opening session of the new parliament.
He starts his second term immediately. In 2018, Castro will be 86.
The Cuban President Raul Casto says he will retire at the end of his next term.
He has just been sworn in for his second term as President which will expire in five years.
A top Cuban official ruled out political change inthe Communist nation despite the Pope's call for renewal and a better society.
Cuba's economic czar and member of President Raul Castro's ministerialcouncil, Marino Murillo, said it is changing its economy but there will not be political reform.