OAKLAND, Iowa -- A fire erupted on a school bus after it backed into a ditch in western Iowa early Tuesday, killing a 16-year-old student and the bus driver, investigators said. No one else was on the bus when the fire erupted around 7 a.m. southeast of Oakland, which is about 35 miles east of Omaha, Nebraska.

Investigators said the bus caught fire after it backed out of a farm driveway and into a ditch across the road. The bus was engulfed in flames when firefighters arrived.

The remains of the driver and a student were found after the fire was extinguished, Pottawattamie County Sheriff's Lt. Rob Ambrose said. The driver was identified as Donald Hendricks, 74, of Carson, Iowa. The student was identified as Megan Klindt, 16. She lived at the farm where the fire happened.

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The cause of the fire remains under investigation. Schools Superintendent Timothy Mitchell said in a statement that the district was cooperating, CBS affiliate KMTV reports.

Initial reports on the fire indicated that as many as 20 people may have been on the bus, but Ambrose said only the two who were killed were on the bus at the time of the fire.

The bus was from the Riverside Community School District, which has about 700 students form around the region.

Mitchell said grief counselors were available Tuesday to help students and staff cope with the deaths. The district didn't cancel classes following news of the fire, but it postponed basketball games scheduled for Tuesday evening.