South Africa's "Blade Runner" Oscar Pistorius was found guilty on Thursday of murdering his girlfriend, in an appeal court ruling that could see him sent back to prison for up to 15 years.

The Supreme Court upgraded the 29-year-old Paralympian's sentence on appeal to murder from "culpable homicide", for which he had received a five-year sentence.

Pistorius was released on parole on October 19, having spent one day less than a year in prison for shooting dead model Reeva Steenkamp on Valentine's Day 2013. He was meant to serve the rest of his sentence under house arrest.

The athlete, known for the carbon fibre prosthetic blades he uses when running, will be sentenced for the new murder conviction by a lower court at a date still to be determined.

It is likely his lawyers could argue that his physical disability and mental stress should be considered as mitigating circumstances.

Prosecutors appealed against the original ruling, saying Pistorius should be convicted of murder for firing four shots through a locked toilet door, in a case that attracted worldwide interest and continues to fascinate and divide South Africa.

"This case involves a human tragedy of Shakespearean proportions," Judge Eric Leach said as he started reading the ruling.

"A young man overcomes huge physical disabilities to reach Olympian heights as an athlete. In doing so he becomes an international celebrity, he meets a young woman of great natural beauty and a successful model, romance blossoms, and then, ironically on Valentine's Day, all is destroyed when he takes her life."

Leach added that "as a matter of common sense, at the time the fatal shots were fired the possibility of the death of a person behind the door was clearly an obvious result."

State prosecutors say Pistorius intended to kill Steenkamp and that she fled to the toilet during a row. Pistorius denies deliberately killing Steenkamp, saying he mistook her for an intruder at his home.

The case has prompted a fierce debate in a country beset by high levels of violent crime. Some rights groups say the white track star got preferential treatment.

ERROR OF JUDGEMENT

At the original trial last year, Judge Thokozile Masipa ruled that the state had failed to prove intent or "dolus eventualis", a legal concept that centres on a person being held responsible for the foreseeable consequences of their actions.

Dolus eventualis refers to whether a person foresees the possibility that his or her action will cause death but carries on regardless.

Some legal experts were worried that the verdict by Judge Masipa could have set a bad legal precedent in a country with one of the highest crime rates in the world.

"That was an error of judgement by the trial court ... He had intention to kill regardless of who was behind the door. That should have been the conviction of the trial court," Mahlatsi Malaka, a private advocate in Bloemfontein said.

Pistorius, whose lower legs were amputated when he was a baby but who went on to become a global sporting hero, was not at the court session in Bloemfontein, some 400 km (250 miles) southwest of Johannesburg.

Anneliese Burgess, the Pistorius family's spokeswoman, said the family would wait for lawyers advice on what to do next.

The athlete has been living with his uncle in a wealthy suburb in the capital Pretoria since being freed on parole.

Steenkamp's mother June, who has said she does not want retribution, attended the court session. She shed tears as she left the court after the new judgement was handed down.

Barry Steenkamp, Reeva's father, welcomed the new verdict.

"It's a big relief. I feel it's a fair decision that the judge gave," Steenkamp said in a brief interview on local television station ANN7, before breaking down in tears.

Members of the ruling African National Congress party's Women's League supported the verdict. They have attended the court sessions in solidarity with Steenkamp's family and in support of women's rights. - Reuters