Prosecutors to appeal sentence and conviction of Oscar Pistorius

South African prosecutors say they will appeal both the conviction and sentence of killer Paralympian Oscar Pistorius.

"NPA (National Prosecuting Authority) will be appealing both the conviction and sentence," spokesman Nathi Mncube said.

Pistorius began a five-year prison stretch last week after being found guilty of culpable homicide, but not guilty of a more serious charge of murder.

The state had sought to prove that Pistorius deliberately shot his girlfriend, 29-year-old Reeva Steenkamp, dead on Valentine's Day last year.

But trial judge Thokozile Masipa found there was not enough evidence to convict the 27-year-old of premeditated murder.

Details of the appeal have not yet released, but South African criminal lawyers have expressed shock that Masipa found Pistorius could not have foreseen that someone would die when he fired the shots.

Legal experts complained that it could open the door to systematic abuse of the legal system, or to people believing it would be okay to shoot in an irresponsible manner.

Steenkamp was shot four times through a locked toilet door at Pistorius's upmarket Pretoria home in the early hours of Valentine's Day.

The Paralympic and Olympic athlete alternatively said he believed there was an intruder and that he did not consciously fire his pistol.

South Africans had also criticised Masipa's five-year sentence as too lenient after it emerged Pistorius may be eligible for parole in less than a year.