Charges are believed to allege that he shot his gun out of car sunroof and accidentally fired friend's gun at restaurant

Oscar Pistorius has been indicted on two new gun-related charges, which are believed to allege that he recklessly shot his gun out of the open sunroof of a car last year and fired someone else's handgun at a restaurant weeks before he killed his girlfriend Reeva Steenkamp.

The double-amputee Olympian has already been indicted on a main charge of murder for Steenkamp's shooting in February and a charge of illegal possession of ammunition in his Pretoria home.

It is likely he will face all four charges at his trial starting in March, although his lawyers can argue against the new charges being added to his current indictment as the offences are alleged to have taken place in Johannesburg, which falls under a different court jurisdiction.

South Africa's national prosecution spokesman, Nathi Mncube, declined to give the exact details of the new charges, saying only that they "relate to the contravention of the firearms act".

Mncube said there had been no indication from Pistorius's lawyers as to whether they would seek to keep the cases separate. South Africa's director of public prosecutions granted permission to add the new charges last month.

According to reports in South Africa, Pistorius is alleged to have fired his own licensed 9mm handgun – the gun used to kill Steenkamp – out of the open sunroof of a car in Johannesburg while travelling with friends last year.

In January, weeks before Steenkamp's shooting death, Pistorius is alleged to have accidentally shot a friend's gun under the table at a Johannesburg restaurant, apparently while admiring it. For both alleged offences he could be charged with public endangerment and damage to property.

He already faces a possible life sentence with a minimum of 25 years in prison if convicted of the premeditated murder of Steenkamp. Pistorius says he shot her by mistake thinking she was a dangerous intruder in his house.