MINNEAPOLIS — Investigators said they cannot determine what caused an explosion and fire that damaged a building housing four apartments in south Minneapolis.

According to the Minneapolis Arson Unit, the fire originated in the living room of a first-floor unit. But fire officials say the cause is considered to be undetermined.

Authorities said nobody was home when the explosion occurred Tuesday afternoon. But, a dog was killed in the blast.

One tenant, Rob Ayott, said he lost everything he owns in the fire, including his artwork, violin and collection of action figures.