OAKLAND, Iowa (AP) — Authorities say a fire aboard an Iowa school bus has killed a student and the bus driver.

Investigators say no one else was on the bus when the fire erupted around 7 a.m. Tuesday southeast of Oakland, which is about 35 miles (56 kilometers) east of Omaha, Nebraska.

Pottawattamie County Sheriff's Lt. Rob Ambrose says the remains of the driver and a student were found after the fire was extinguished. The ages and names of the victims weren't immediately released.

Ambrose says no one else was on the bus at the time.

The bus caught fire after it backed out of a farm driveway and into a ditch across the road. The cause of the fire remains under investigation.

The bus was from the Riverside Community School District.