An "extremely remorseful" elderly man admitted Friday he accidentally started a brush fire that exploded into a wall of flames and destroyed 29 homes when he improperly discarded fireplace ashes at his home south of town, fire officials said.

Reno Fire Chief Michael Hernandez told reporters that investigators determined the cause of the blaze that burned nearly 3,200 acres and forced the evacuation of up to 10,000 people at the fire's peak Thursday evening.

"He came forward on his own accord," Hernandez said.

"He has given statements to our investigators as well as law enforcement officers. He is extremely remorseful," he said.

Washoe County Sheriff Mike Haley the case will be forwarded to the district attorney for consideration of formal charges. In addition to the potential for charges as serious as felony arson, the man could be ordered to pay the cost of fighting the fire, which already totals $690,000, authorities said.

Washoe County Manager Katy Singlaub said she expects costs to rise into the millions of dollars.

Investigators had tracked the origin of the fire to a location in East Lake on the north end of the Washoe Valley, where the man lives.

Hernandez said he couldn't comment more other than to say the man was elderly.

Hernandez also confirmed a 93-year-old woman had been found dead in a home that had suffered fire damage Thursday but they have not confirmed the cause of death.