JOHANNESBURG -- Olympian Oscar Pistorius, in jail for murdering his girlfriend, was bruised in an altercation with another inmate over telephone use, a South African prison spokesman confirmed Tuesday.

Pistorius sustained a minor injury in an alleged assault at the Attridgevill Correctional Centre last week, Singabakho Nxumalo of the Department of Correctional Services told The Associated Press. Pistorius had a medical checkup and was found to have a bruise, said Nxumalo, who added that the incident is being investigated.

"The injury is minor but we at the department take incidents like this seriously and want to prevent any altercations," said Nxumalo.

The disagreement broke out between Pistorius and another inmate over use of a public telephone, he said.

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Pistorius, a double amputee runner who won worldwide acclaim winning in the Paralympics and competing in the Olympics, is serving a 13-year sentence for the murder of his girlfriend Reeva Steenkamp. Pistorius shot her dead in his home on Valentine's Day 2013 and claimed he thought she was an intruder.