SEATTLE — Two US firefighters have been killed and a third wounded after a man intentionally started a fire and began shooting at first responders in a "total ambush" which lasted several hours, authorities said.

A man found dead on Canfield Mountain in Idaho is believed to be the only shooter involved in the deadly ambush on Sunday..

The man is believed to have started a brush fire before shooting at responding firefighters, the Kootenai County sheriff said.

The gunman, who investigators said acted alone, began shooting after crews responded to a fire at Canfield Mountain, just north of Coeur d'Alene, Idaho, Sunday afternoon.

Investigators are likely working to understand the motivation of the Idaho suspect who they believe started a brush fire before shooting at responding firefighters in what authorities describe as a planned ambush, a former intelligence official told CNN.

“Right now, behind the scenes, there’s a lot of work going on to really understand who this individual is and what motivated them to carry out this attack,” Shawn Turner, former US national intelligence communications director, said Monday.

Law enforcement officers and firefighters came under sniper fire during the incident and a Special Weapons and Tactics (SWAT) team later "located a deceased male" close to where the attack took place.

The fire grew to 20 acres after it was first reported and continued to burn into Sunday night, Sheriff Bob Norris said. — Agencies