Fire officials in Coeur d'Alene are investigating a Sunday night fire that destroyed an under-construction duplex and damaged three nearby homes.

Police Sgt. Brett Walton said two people were seen leaving the duplex Sunday evening and the fire started a short time later, but the cause is not known yet.

Deputy Fire Chief Glenn Lauper said the fire appeared to have started upstairs in one of the duplex units before spreading to the other unit. The heat from the fire melted the siding on three nearby homes.

One firefighter sustained a sprained ankle but no other injuries were reported.