The Forest Service said in a news release Thursday that investigators are focused on fires that started Oct. 28 or later. The two largest are the Tellico fire, which has burned about 10 square miles and the Maple Springs fire, which has burned nearly 8 square miles.
The fires are among those in the southern Appalachian mountains, where a relentless drought has turned pine trees into matchsticks torches and forced evacuations in dozens of communities.
Arson arrests have been made in Tennessee and Kentucky.
Gov. Pat McCrory declared a state of emergency in 25 counties in western North Carolina on Thursday, freeing up additional state resources to fight the fire.