"The UAZ car was parked next to the building," a spokesman for the breakaway Georgian republic's information and press committee said. "The blast seriously damaged the building and broke window panes in neighboring houses within a 500 m radius."
According to the spokesman, the car had been taken to the capital after it was removed from a village in one of the so-called buffer zones controlled by Russian peacekeepers since the brief military conflict between Russia and Georgia over South Ossetia in August.
The official said six people were killed in the blast and one person died from sustained shrapnel wounds in a local hospital.
Meanwhile, the head of the Leninigorski district in South Ossetia, Anatoly Margiyev, reportedly escaped an alleged attempt on his life when a roadside bomb exploded near his car on Friday.
"Margiyev was in his car, when an Ural truck, which followed behind, was caught in a roadside bomb explosion," Emergencies Ministry spokesman Inal Pliyev said. "The driver of the truck and a passenger were wounded and received medical treatment."
The vehicle convoy was heading to Tskhinvali to collect humanitarian supplies.
Pliyev said that Margiyev had received a number of death threats in the past, demanding that he quit his office.
Local police have launched an investigation into the suspected assassination attempt.