Pistorius, who pleaded not guilty at his trial in 2014, has always denied killing Steenkamp in a rage, saying he was trying to protect her
South African prosecutors said Thursday they would push for a longer sentence for South African Olympic and Paralympic sprinter Oscar Pistorius, describing his six-year jail term for murdering his girlfriend Reeva Steenkamp as "shockingly too lenient".
"The sentence of six years imprisonment, in all the circumstances, is disproportionate to the crime of murder committed (and) shockingly too lenient," the National Prosecuting Authority said in a strongly worded statement.
The NPA added that the sentence was "an injustice and has the potential to bring the administration of justice into disrepute", saying that it would file papers to apply for leave to appeal on Thursday.
When he was sentenced earlier this month, Pistorius' lawyers said the Paralympic athlete would not appeal against the term, which was criticised by many activists as too short.
High Court judge Thokozile Masipa listed several mitigating factors for sentencing him to less than half the minimum 15-year term for murder, including the athlete's claim he believed he was shooting an intruder.
"He cannot be at peace. I`m of the view that a long term of imprisonment will not serve justice," Masipa said.
The sister of South African Paralympic star said that she was "grateful" to the judge. "The thing I'm most grateful (for) and the thing I really appreciate is the emphasis she made to distinguish a difference between the facts and the truth in terms of this is not a gender-based violence situation. It's a terrible accident where Oscar had no intention of shooting Reeva," Aimee Pistorius said in an interview with the eNCA television news channel.
Celebrated sprint champion Pistorius shot Steenkamp, a model and law graduate, in the early hours of Valentine's Day in 2013, saying he mistook her for a burglar when he fired four times through the door of his bedroom toilet.
The 29-year old was previously a role model for disabled people worldwide and is now being held in Kgosi Mampuru II prison in Pretoria.
He was released from the same jail last October after serving one year of a five-year term for culpable homicide - the equivalent of manslaughter.
But an appeals court upgraded his conviction to murder in December.
At a hearing in June, Pistorius, sobbing heavily, hobbled on his stumps across the courtroom to demonstrate his physical vulnerability.
His lawyers had argued he should not be returned to jail on account of an anxiety disorder and depression.
Pistorius, who pleaded not guilty at his trial in 2014, has always denied killing Steenkamp in a rage, saying he was trying to protect her.
The Supreme Court of Appeal last year ruled he was guilty of murder, irrespective of who he believed was behind the door, when he opened fire with a high-calibre pistol he kept under his bed.
The year before he killed Steenkamp, Pistorius became the first double-amputee to race at Olympic level when he appeared at the London 2012 games.