Johannesburg — A fresh investigation has begun into the disappearance of two men reportedly last seen with former president Nelson Mandela's wife, Winnie Madikizela-Mandela.

National Prosecuting Authority spokesman Makhosini Nkosi said it had "recently obtained information" about Lolo Sono and Siboniso Shabalala, who went missing in 1988.

He said burial sites were being examined to find the remains of the pair, but could not confirm reports that they were linked to Madikizela-Mandela.

"The investigations into this case are still ongoing... No exact burial sites have yet been confirmed or excavated," he said in a statement.

Associated Press reported that the two had last been seen at Madikizela-Mandela's home in Soweto, Johannesburg, in November that year.

Madikizela-Mandela was convicted in 1991 of kidnapping four young men and taking part in assaults on them. She was initially sentenced to six years in jail but on appeal was ordered to pay a fine.

Nkosi said a missing persons task team in the NPA had been mandated to trace the missing two.

"It is standard practice for the... team to take DNA from family members of missing persons... so that DNA testing can be done... This has been done with the Sono and Shabalala families," he said.

"Should the remains of Lolo Sono and Siboniso Shabalala be located and identified through DNA, these remains will be formally handed to the two families by the department of justice and constitutional development..."