A high court in South Africa increased Oscar Pistorius' prison sentence Friday to 13 years and five months for the murder of his girlfriend, Reeva Steenkamp.

South Africa's Supreme Court of Appeal issued the ruling after the prosecution appealed his previous sentence of six years as too lenient.

The former Olympic and Paralympic sprinter killed Steenkamp at his home in an upscale Pretoria neighborhood in the early hours of Valentine's Day in 2013 -- an act he says was an accident after he mistook her for an intruder. The prosecution called it a deliberate act after the two had an argument.

Prosecutor Gerrie Nel has argued that Pistorius' sentence was "shockingly lenient" while the defense has said the appeal for a higher sentence should be dismissed.

Pistorius was initially convicted of manslaughter in 2014 after months of hearings, but a higher court changed that to murder last year.

The judge surprised many when she sentenced Pistorius to six years. The minimum sentence for murder in South Africa is 15 years, but individual judges can lower the sentence if there are "substantial and compelling" reasons to do so.

During Pistorius' initial sentencing, the judge cited mitigating circumstances for the lesser punishment, saying Pistorius was genuinely remorseful and a good candidate for rehabilitation.

She described him as a "fallen hero" who will never be at peace.

Agencies