The first lawsuit filed in connection with a wildfire that destroyed more than 1,000 homes and other buildings in suburban Denver claims that sparks from a power line started December's blaze.

The lawsuit filed late last week against Xcel Energy says that its power lines and equipment were a "substantial factor" in the cause, origin and continuation of the wildfire, which was fanned by intense winds. It says witnesses saw a fire igniting near a power line in the area where authorities say the wildfire started, with one witness filming sparks flying from a malfunctioning power line and igniting a fire on the ground that became the wildfire.

A spokesperson for Minneapolis-based Xcel, Michelle Aguayo, said the company was reviewing the lawsuit but said it has not seen evidence that its equipment ignited the fire.

"Our own investigation shows that our equipment in the area of the fire was properly maintained and inspected, consistent with our high standards," she said.

Authorities have not finished their investigation into what caused the fire, blamed for at least one death, and they said Thursday that the work is expected to take several more months. The Boulder County Sheriff's Office declined to provide any details about the findings so far, but it has has previously said it was investigating "any and all potential causes," including power lines, human activity and old coal mines in the area where coal continues to burn underground.

The lawsuit seeks to be made a class action case, representing people affected by the fire. It was brought by two related businesses, including a store near where the sparking power line was reported, and an anonymous married couple. The store survived the fire, and the lawsuit does not provide specific details about how the couple was harmed by the fire.