四位美国总统将出席曼德拉悼念仪式

World leaders are headed to South Africa for Tuesday's memorial service for Nelson Mandela, the anti-apartheid leader who died last week at the age of 95.

U.S. President Barack Obama left Washington Monday morning, accompanied by first lady Michelle Obama, and former President George W. Bush and his wife Laura. Former presidents Bill Clinton and Jimmy Carter are also traveling separately to Johannesburg where the service will be held in the Soccer City stadium, the site of the 2010 World Cup.

George H.W. Bush is the only living former U.S. president who will not attend the event.  His spokesman said the 89-year-old Mr. Bush is no longer able to travel long distances.  

South African Foreign Minister Maite Knoana-Mashabane says there has been "uNPRecedented interest" from world leaders who want to attend the event, which will be held under heavy security. 

British Prime Minister David Cameron, Iranian President Hassan Rouhani, Cuban President Raul Castro and  U.N. Secretary-General Ban Ki-moon are among others also expected to attend the service for Mr. Mandela, who emerged from 27 years in prison to become South Africa's first black president.