Several drone sightings near firefighting aircraft are fueling calls for more oversight and self-policing in the skies.

The U.S. Forest Service has tallied 13 wildfires in which suspected drones interfered with firefighting aircraft this year, including 11 since late June. That's up from four fires last year and only scattered incidents before.

Last month, the sighting of five drones in a wildfire that closed Interstate 15 in Southern California and destroyed numerous vehicles grounded crews for 20 minutes.

Nine drone sightings this year were in California. The others were in Colorado, Minnesota, Utah and Washington.

Firefighting agencies have introduced public service announcements to warn drone hobbyists. Lawmakers are seeking stiffer penalties for interfering.