Authorities say a woman and her 6-year-old granddaughter were the two people killed in a fire at a Middlesex County duplex this week.

But it's still not clear what caused the fire that was reported around 2:20 p.m. Wednesday in Edison.

Fifty-six-year-old Kathleen O’Callahan was pronounced dead at the scene, while her granddaughter died at a hospital later that day. The girl's name has not been released.

Authorities have not said whether either victim lived at the Jill Court home or what caused their deaths. A dog was also killed in the fire.

The cause of the blaze remains under investigation.