The key is among several pieces of memorabilia linked to Mr Mandela being sold by Guernsey's - an auction house in New York on 28 January.

Most of the items have been provided by the former president's family to help raise money for a museum and garden around his grave in Qunu, a village in eastern South Africa where Mr Mandela was born.

A former prison officer, who became friends with Mr Mandela, is selling the key.

'Key belongs to people of South Africa'

But South Africa's minister for sport, arts and culture, Nathi Mthethwa, said in a statement that the "key belongs to the people of South Africa and is not anyone's personal belonging".

"It is unfathomable for Guernsey's, which is clearly aware of the painful history of our country and the symbolism of the key, to consider auctioning the key without any consultation with the South African government, the heritage authorities in South Africa and Robben Island Museum," Mr Mthethwa added.

The auction house said that all the proceeds will raise funds to help build a 24-acre memorial garden and museum around Mr Mandela's burial site.

Makaziwe Mandela-Amuah, Mr Mandela's oldest daughter, approached Guernsey's to hold the auction to help build the garden, Arlan Ettinger, president of the auction house, told The Associated Press.

The 33 objects to be auctioned include one of Mr Mandela's colourful shirts, gifts from former US presidents Barack Obama and George W Bush, as well as items that he signed and artwork.

Christo Brand, the prison officer who became friends with Nelson Mandela

The key to his former jail cell is one of three items put up for sale by Christo Brand, who was a prison officer at Robben Island - where Mandela was held because of his opposition to apartheid between 1964 and 1982.

A draft of South Africa's constitution that Mr Mandela inscribed to Mr Brand and an exercise bicycle he used were also provided for the auction by Mr Brand.

Mr Brand's representative could not be reached for comment.

The key has been in Mr Brand's possession for many years and has been exhibited internationally, said Mr Ettinger.

Mr Mandela's daughter has approved its sale and a portion of the proceeds will go to the garden fund, he said.

A timeline of Mr Mandela's life

"The key locked up Mr Mandela for his opposition to racial oppression and that was horrendous," Mr Ettinger added.

"The key also freed him and he went from prisoner to president of South Africa and became the inspiration for millions of people around the world."

Mthethwa, the minister of culture, said he will take action to stop the key's auction.