NELSON Mandela's ex-wife Winnie is shocked to learn South African prosecutors may probe her over the deaths of two anti-apartheid youths who went missing almost 25 years ago, one of her lawyers says.

Last week, the skeletons of what are believed to be the remains of Corlett "Lolo" Sono, 21, and Siboniso Anthony Shabalala, 19, were exhumed in a Soweto cemetery.

The pair, who served as couriers for the anti-apartheid military wing of the African National Congress, were last seen alive at Winnie Madikizela-Mandela's home in 1988.

The uncovered remains had multiple stab wounds to them and had been buried as unidentified persons among paupers.

Police are still awaiting forensic and DNA tests to be carried out on the skeletons, but if the men's identities are confirmed, prosecutors have said they will consider filing charges against Madikizela-Mandela.

In the statement dated March 16 and sent to AFP, her lawyer, Pops Mageza, said his client wished "to express her surprise and shock ... that there are processes currently under way which will lead to her prosecution for the deaths" of Sono and Shabalala.

"To her knowledge, these are matters that have already been comprehensively dealt with," the lawyer wrote.

The two activists' disappearance was linked to Madikizela-Mandela during the country's Truth and Reconciliation Commission set up after 1994's democracy to address apartheid atrocities.

The body's final report concluded she "must accept responsibility for the disappearance" of the pair who were last seen alive at her home.

Madikizela-Mandela, whose husband was jailed at the time, denied any involvement in the killings.

But Sono's father told a commission hearing the last time he had seen his son was in Madikizela-Mandela's company, saying his son had been accused of spying.

During the 1980s, Madikizela-Mandela surrounded herself with a ruthless band of bodyguards known as the Mandela United Football Club.

She was convicted in 1991 on kidnapping and assault charges over the killing of a young activist three years earlier. The jail term was reduced to a fine.