The Mandela family has reacted angrily after the former South African leader's voice was used in an election advert for the country's main opposition.

In the ad, posted on YouTube, a young woman is in a polling booth considering voting for the governing ANC.

As Nelson Mandela's voice is heard calling for justice, peace, work and bread, she then decides to vote for the Democratic Alliance (DA) instead.

Chief Mandla Mandela accused the DA of abusing his grandfather's name.

"The DA is doing it to benefit a party which Mandela was not a member of," he told the ANN7 news network.

In other comments, Mandla Mandela, who is himself a member of parliament for the African National Congress (ANC), said the DA was seeking to "preserve white privilege" and demanded the ad be withdrawn.

The DA has defended using the voice of the former president, who was a long-standing ANC member, saying "this great man stood for a non-racial South Africa".

"The DA is the only party able to take South Africa to the non-racial future it needs. To say that Mandela does not belong to all South Africans is atrocious," said spokesperson Refiloe Nt'sekhe.

The DA has based its electoral campaign around promises to fight corruption and improve the country's economic prospects.

But it has faced criticism in the South African media in recent weeks over racist remarks made by its members.

South Africans will vote next month in what are expected to be closely contested municipal elections.