South African prosecutors called Oscar Pistorius's five-year manslaughter sentence for killing his girlfriend "shockingly light" and "inappropriate," as they launched a formal appeal on Tuesday.
State attorneys, pressing for a murder conviction and a harsher sentence for the Olympic star, lodged papers at the Pretoria High Court, signalling a new round in the high-profile legal fight.
"The sentence of five years imprisonment... for the murder of Reeva Steenkamp in the circumstances of this case is shockingly light, inappropriate and would not have been imposed by any reasonable court," the National Prosecuting Authority said in its filing.
After a sensational trial that lasted more seven months, Pistorius was found guilty of culpable homicide -- a count equivalent to manslaughter -- for shooting dead the 29-year-old model on Valentine's Day 2013.
Two weeks ago, the Paralympian was handed the five-year sentence which he started serving immediately.
Under South African law Pistorius could be eligible to complete just one-sixth of his sentence in jail.
"In effect the sentence imposed on the accused means that he will qualify to be released on correctional supervision after serving a mere 10 months," said the court papers.
During his trial, Pistorius admitted to shooting Steenkamp four times through a locked toilet door at his upmarket Pretoria home, but said he thought he was firing at an intruder.
Prosecutors alleged that he shot Steenkamp deliberately after an argument.
High Court Judge Thokozile Masipa found there was not enough evidence to convict the 27-year-old Paralympic and Olympic athlete of premeditated murder.
But the prosecutors say Masipa "erred in over-emphasising the personal circumstances of the accused and the fact that he was suffering from post-traumatic stress, was anxious and 'seems remorseful'".
They also believe the judge did not appropriately take into account Pistorius's actions.
"There is a reasonable prospect that another court may come to a different finding" with regards to the sentence imposed or "in fact overturn the sentence", they said.
- Stage set for new legal battle -
Pistorius is currently serving his sentence in the hospital section of a Pretoria prison.
The date for the appeal has not been set and neither the defence nor the Pistorius family were immediately available to comment.
According to the rules of Supreme Court of Appeal, the defence has one month to file an answering affidavit.
The prosecution also voiced dissatisfaction with the court's handling of circumstantial evidence during the trial.
They say it "did not discuss, accept or reject the circumstantial evidence rendering the version of the accused impossible".
They maintain that Pistorius acted with gross negligence in firing the gun, noting the use of the lethal hollow-point bullets through a small toilet cubicle.
During his trial, the prosecution painted a dark picture of the sports star, presenting a dangerously volatile young man with a penchant for guns, beautiful women and fast cars.
National Prosecuting Authority spokesman Nathi Mncube said the application to appeal was expected to be heard by the same judge, Masipa, at the High Court.
"After presenting our case, the judge will either grant or reject our application," said Mncube.
"If it's granted, the case will then be heard by the Supreme Court of Appeal."
Mncube stressed that in the event that Masipa did not grant the appeal, the state had an option to petition the Supreme Court directly to hear the case.
Cases heard by the Supreme Court, located in South Africa's central city of Bloemfontein, are presided by a panel of three to five judges, depending on the nature of a case.
Pistorius became famous for becoming the first double amputee Paralympian to compete against able-bodied athletes at the 2012 London Olympics.
His imprisonment has curtailed his career, with the International Paralympic Committee banning him from competition for five years.
Both Pistorius's and Steenkamp's families accepted the decision by the prosecutors to appeal when it was announced last week.
The Steenkamps have said they no longer plan to pursue a civil case against the athlete.