A sentencing hearing for South African athlete Oscar Pistorius, who murdered his girlfriend, Reeva Steenkamp, is due to start in Pretoria.

He faces a jail term of at least 15 years, but his sentence can be reduced due to time already spent in prison and mitigating factors.

A sentence is expected by Friday. He will have no right to appeal.

Pistorius, 29, killed Ms Steenkamp in February 2013 after firing four times through a locked toilet door.

The athlete has always maintained he believed he was shooting at an intruder.

He was initially sentenced to five years for manslaughter, but the conviction was upgraded to murder in December following an appeal by the prosecution.

Original trial judge Thokozile Masipa will hear arguments from both prosecution and defence this week. The Paralympic athlete may testify.

Reeva Steenkamp's father, Barry, who has been absent throughout the case due to poor health, may also appear in court.

Experts say a custodial sentence seems almost unavoidable but factors such as his mental fragility, disability and good behaviour might lead to a reduced jail term.

Pistorius will not be able to appeal, as a top court ruled in March that he had exhausted all his legal options.

He was released from prison last October after almost a year in jail and allowed to serve out the remainder of his initial sentence under house arrest on his uncle's property in Pretoria.

The South African made history by becoming the first amputee sprinter to compete at the Olympics, in London in 2012.

He competed in the 400m, wearing carbon-fibre blades to run against able-bodied athletes.