BOSTON -- A South Boston fire that claimed the lives of two girls was intentionally set, the Boston Fire Investigation Unit announced Tuesday.

Acia Johnson, 14, and 2-year-old Sophia Johnson died in the April 6 fire at 154 West Sixth St. The victims were found trapped under debris in a rear upper room of the home.

Responding officers found the front of the residence engulfed in flames that were rapidly spreading to adjacent dwellings when they arrived at the home on the night of the fire.

Earlier Tuesday, the girls' deaths were ruled homicide by smoke inhalation and thermal injuries.

The Boston police continue to actively investigate the facts and circumstances surrounding the fire. Anyone who has information is urged to contact the Homicide Unit at 617- 343-4470 or the Crime Stoppers Tip Line at 800-494-TIPS.