Prosecutors in South Africa said they plan to appeal Oscar Pistorius' six-year jail sentence for the murder of his girlfriend, calling it "shockingly" lenient, reports NBC News.

The double-amputee Olympic champion was sentenced on July 6 for the Valentine's Day 2013 killing at his home.

Prosecutors had sought 15 years in prison — the prescribed minimum sentence for murder in South Africa — but the judge cited mitigating circumstances in Pistorius' case to giving him a lesser sentence.

The country's National Prosecuting Authority announced it would file appeal papers on Thursday.

"We respectfully submit that the sentence … is disproportionate … shockingly too lenient, and has accordingly resulted in an injustice," the NPA announced.

The filing will mark the second time the athlete's case has been appealed by prosecutors.

Pistorius was initially acquitted of murder — telling his trial that he shot Steenkamp by accident after mistaking her for an intruder — but later convicted after the state challenged that verdict.

Steenkamp's parents, meanwhile, said they were focused on launching a non-profit in their daughter's name to campaign against domestic violence.

"June and Barry have always fully supported [prosecution lawyer] Gerrie Nel and his team's fight for justice for Reeva," they said in a statement. "As they have no input in the decision of the state to appeal, they are focusing their energy on the upcoming official media launch of The Reeva Rebecca Steenkamp Foundation."