SPOKANE COUNTY, Wash. -

The Spokane County Sheriff's Office is investigating a suspicious fire in South Spokane County.

The fire started just before 4:30 a.m. Friday, near South Kiesling Road and East Big Rock Road.

Deputies said they received reports of a brush fire near the intersection. When firefighters arrived, the brush fire had burned about a quarter of an acre, but a nearby bus that was sitting on the side of the road was fully engulfed in flames.

Upon further investigation, they determined the fire had started on the bus and spread to the brush.

Spokane County Sheriff's Office deputies said the bus was reported stolen out of Spokane Thursday. It was privately-owned, but had one time belonged to the Deer Park School District. They said they don't know what caused the fire on the bus.