Six-time Paralympic champion Oscar Pistorius was reportedly left fuming in prison when he discovered that he could still face a murder conviction.

The 28-year-old is serving a five-year sentence for the culpable homicide of girlfriend Reeva Steenkamp, whom he shot dead through a toilet door at his home in Pretoria, South Africa in the early hours of Valentine's Day last year.

On Wednesday, Judge Thokozile Masipa, who delivered the original verdict, granted prosecutors leave to appeal the conviction, but not the sentence.

This means that Pistorius could potentially face a jail term of 15 years, which he initially escaped when the judge believed the double amputee's claims that he mistook Steenkamp for an intruder when he fired four gunshots.

According to the Daily Star, Pistorius vented his anger by stomping around the prison when he discovered the news via jail radio.

A fellow prisoner in the Kgosi Mampuru II jail is quoted as saying: "Oscar got up and stomped. He went straight to the gym. He started lifting weights like it was going out of fashion. He is pissed off."

It could be a year before it is discovered whether an appeal has been successful or not.