JOHANNESBURG, Aug 17, South African state prosecutors filed an appeal on Monday against the verdict of culpable homicide passed on Oscar Pistorius for killing his girlfriend, arguing the athlete should have been convicted of murder.

The Paralympic gold medalist admitted 29-year-old killing Reeva Steenkamp in February 2013 by firing four shots into the locked door of a toilet cubicle in what he said was the mistaken belief that an intruder was hiding behind it.

Pistorius, whose lower legs were amputated as a baby, is due to be released on Friday after serving 10 months of a five-year sentence, in line with South Africa's custodial guidelines for non-dangerous prisoners.