Heads of state from around the world, royals, celebrities and tens of thousands of South Africans have converged on FNB Stadium in Johannesburg's Soweto neighborhood to pay tribute to Nelson Mandela, the world’s foremost anti-apartheid leader and a global reconciliation icon, at a memorial service on Tuesday.

In an unparalleled show of international unity, President Barack Obama shared a stage with several other world leaders, including Raul Castro, the president of Cuba, a U.S. foe for more than half a century.

Obama and former President George W. Bush and their wives Michelle Obama and Laura Bush joined other guests such as United Nations Secretary General Ban Ki-moon, British Prime Minister David Cameron and French President Francois Hollande among several others from nations including China and India.

“South Africa, the world thanks you for sharing Mandela with us,” Obama said in his homage to the South African leader, according to a Telegraph report. “His struggle was your struggle. His triumph was your triumph. Madiba would emerge as the last great liberator of the 21st century,” Obama said in an affectionate reference to Mandela by his traditional Xhosa clan name.

“It is hard to eulogize any man ... how much harder to do so for a giant of history, who moved a nation towards justice,” Obama said.

Iranian President Hassan Rouhani was earlier reported to be among those expected for the service, but his name was not on the official list of attendees, media reports said.

Ban who spoke before Obama said, “South Africa has lost a hero, a father. The world has lost a beloved friend and mentor. Mandela was more than one of the greatest leaders of all time.

“This boxer fought throughout his life for each of us. It is the duty of all of us who loved him to keep his memory alive,” Ban said.

Among the celebrities attending the service include talk show host Oprah Winfrey, singers Peter Gabriel and Bono, model Naomi Campbell and entrepreneur Richard Branson, Reuters reported.

The area is under heavy security, and private cars have been banned from the area. Earlier, Israeli Prime Minister Benjamin Netanyahu dropped out of the event citing the high costs involved in security detail and travel.

Archbishop Desmond Tutu, South African President Jacob Zuma and Indian President Pranab Mukherjee, as well as Zimbabwean President Robert Mugabe and former British Prime Minister Tony Blair -- who have traded barbs in the past -- are among the guests attending the event.

“What he did in life, that's what he’s doing in death. He’s bringing people together from all walks of life, from the different sides of opinion, political belief, religion,” Zelda la Grange, Mandela’s former personal assistant, told Reuters.