A fatal fire at an apartment building in Reston is being investigated as a homicide, Fairfax county authorities said Monday.

One person died in the fire, which broke out early Monday morning at an apartment in the 12000 block of Waterside View Drive.

According to officials, firefighters responded to the building, located near the Fairfax County Parkway, around 6:20 a.m. The blaze was traced to a locked second-floor unit. Firefighters forced their way inside and found the body of an adult woman inside one of the rooms.

The woman, whose identity has not been released, was pronounced dead at the scene, officials said.

Neither the cause of death nor the cause of the fire has been determined. Police did not say what led them to investigate the incident as a homicide.

The fire was confined to the apartment where the woman’s body was found, but there was smoke damage to other units in the building, officials said.

The incident remains under investigation.