Oscar Pistorius, the former Paralympic champion and convicted murderer, has been injured in a prison brawl over the use of a public phone, a South African official has said.

The double amputee – who is serving a 13-year jail term for the murder of his girlfriend Reeva Steenkamp – was left with a bruise after “an altercation with another inmate” on 6 December, according to the Department of Correctional Services.

“Oscar Pistorius sustained a bruise following an alleged incident with another inmate over the use of a public phone in the special care unit where both offenders are detained at Attridgeville correctional centre,” a spokesman, Singabakho Nxumalo, said.

In November 2016 Pistorius was moved to the prison north of the capital, Pretoria, which caters for inmates with physical disabilities.

He killed Steenkamp, a model and law graduate, by firing four bullets from a handgun through a closed toilet door in his luxury home in Pretoria on Valentine’s Day 2013. He claimed he had mistaken her for a burglar.

Last month, the supreme court of appeal more than doubled his original sentence of six years after the state argued that it was unduly lenient.

Nxumalo said an official investigation had been launched into the incident.

There were unconfirmed reports in local media that fellow prisoners were angered by a lengthy Pistorius telephone conversation, leading to a fight.

Pistorius, 31, was originally convicted of culpable homicide – the equivalent of manslaughter – but the appeal court upgraded his conviction to murder.