aftertheending a: World Leader's Gather to Pay Tribute To A 'Giant Of History' Nelson Mandela At The State Memorial Service

Eulogy: U.S. President Barack Obama acknowledges the crowd as he delivers his speech at the memorial service for Nelson Mandela in Johannesburg

Tens of thousands of South Africans have joined dozens of world leaders for the national memorial service for former President Nelson Mandela. The service was held in front of a vociferous crowd in the FNB stadium in Johannesburg.

Relatives: Mr Mandela's ex-wife Winnie Mandela Madikizela (left) and his widow Graca Machel (far right) take their seats in the stadium

US President Barack Obama said Mr Mandela was a "giant of history", describing him as the last great liberator of the 20th Century.

Eulogy: U.S. President Barack Obama delivers his speech at the memorial service for Nelson Mandela at the FNB soccer stadium in Johannesburg

The former South African president died last Thursday, aged 95.

The country is observing a series of commemorations leading up to the funeral on Sunday.

The memorial service, which began at about 12:00 (10:00 GMT), lasted about four hours.

It was one of the biggest gatherings of international dignitaries in recent years, with more than 100 current or former heads of state or government attending.

Fitting setting: A general view of the arena which was the location of Mr Mandela's first speech in Johannesburg after he was released from prison in 1990

There had been fears people would be turned away. But with heavy rain, security and transport issues, and the fact that Tuesday was not declared a national holiday, areas of the 95,000-capacity stadium remained empty.

Introducing the proceedings, the master of ceremonies, Cyril Ramaphosa, said that Mr Mandela's "long walk is over... and he can finally rest".

Current South African President Jacob Zuma made the keynote address but was booed in some parts of the ceremony.

He said Mr Mandela was "one of a kind... a fearless freedom fighter who refused to allow the brutality of the apartheid state to stand in way of the struggle for the liberation of his people".

Historic: The handshake between the leaders of the two Cold War enemies came during a ceremony that focused on Mandela's legacy of reconciliation

Mr Zuma announced he was renaming the Union Buildings in Pretoria, where Mr Mandela will lie in state, as the Mandela Amphitheatre.

Earlier Mr Obama delivered his address, carried on the White House web site, to huge cheers. He said: "It is hard to eulogise any man... how much harder to do so for a giant of history, who moved a nation towards justice."

Giving his condolences: President Obama kisses Nelson Mandela's widow Graca Machel during the memorial service

He said Nelson Mandela had taught the world the power of action and the power of ideas, and that it had taken a man like Mr Mandela to free not only the prisoner but also the jailer.

Mr Obama said: "We will never see the likes of Nelson Mandela again. While I will always fall short of Madiba (Mr Mandela's clan name), he makes me want to be a better man."

Selfie: David Cameron and Barack Obama took a picture of themselves alongside Denmark's prime minister Helle Thorning Schmidt

On his way to the podium, President Obama shook hands with Cuban President Raul Castro, an unprecedented gesture between the leaders of two nations that have been at loggerheads for more than half a century.