The gunman killed members of his own family, two of the restaurant owner’s children and also the owner, according to Interior Minister Danilo Saranovic.
Mr Saranovic called the incident a “consequence of disturbed interpersonal relations”, according to AFP news agency.
Four people are in a life-threatening condition in hospital after being seriously wounded in the shooting, the agency reported the prime minister as saying.
The suspect had previously been arrested for weapons possession, Reuters news agency reports.
Mass shootings are comparatively rare in the small Balkan nation.
