The explosion on the top floor of the nine-story building ripped through the structure in the city of Shakhty before dawn Monday. One woman was found dead. Two people who were rescued from the wreckage shortly after the blast remained hospitalized in stable condition.
As the search operation continued, emergency crews found the body of an elderly woman early Tuesday. The bodies of a missing middle-aged couple were located later in the day, Vyacheslav Butko, top regional official for Emergency Situations Ministry, told Russian news agencies.
One person still was unaccounted for.
Emergency officials said they expect the search to finish by the end of the day.