Ms Mandela remains a controversial political figure in South Africa

"If we forgave what was done to us in South Africa, is not it possible to forgive?", asked the ex-wife of former South African President Nelson Mandela.

Williams, 51, was sentenced to death in 1981 for the murder of four people.

Co-founder of the notorious Los Angeles Crips street-gang, he denies committing the 1979 murders.

Williams faces death by lethal injection on 13 December at San Quentin prison, north of San Francisco.

While in jail, he has won praise for his anti-gang books, earning several Nobel Peace Prize nominations for his teachings. He has generated a public campaign calling for clemency.

'Regret'

California's Governor Arnold Schwarzenegger is expected to hold a clemency review on Thursday.

At a news conference, Ms Mandela said that, in a recent visit she made to the US, Mr Schwarzenegger had refused to meet her because it conflicted with the law.

Williams co-founded the notorious Crips gang

"I regret it very much that a man who has wined and dined with comrade Mandela in his home would react in this manner," she added.

The anti-apartheid campaigner also said that if Williams was executed, she would follow through on his request that he be buried or have his ashes scattered in South Africa.

"I would be honoured to carry out his wishes."

Ms Mandela remains a controversial political figure in South Africa following her divorce from Nelson Mandela and convictions for kidnapping and fraud.

She is the latest high-profile personality to call for clemency for Williams.