Correctional Services Minister S'bu Ndebele said officials were too slow to protect convicted killer Clive Derby-Lewis from being attacked for a second time, according to a report.
"Perhaps we should have acted earlier when he was attacked," Ndebele was quoted by The Star newspaper as saying at an ANC briefing.
"Inmates go to prison as punishment, not to be punished further... We take a serious view on that... Nobody must take the law into their own hands. We condemn it in the strongest terms."
Derby-Lewis was taken to hospital on Sunday after being stabbed by an inmate with a piece of broken glass.
"When Derby-Lewis comes out of hospital he will be placed in a single cell where a repeat of this thing will never happen. We will ensure he is safe."
The 78-year-old was attacked on Sunday at the Kgosi Mampuru Correctional Centre.
In February, Derby-Lewis was attacked with a spoon by another prisoner and suffered lacerations on the head and hand.
He was sentenced to 25 years behind bars for his role in SA Communist Party leader Chris Hani's killing. He has already served almost 20 years. Hani was shot dead in the driveway of his home in 1993.
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