OMAHA, Neb. (AP) — BNSF Railway acknowledged Friday that flooding played a role in a derailment that loosed thousands of gallons of oil into northwest Iowa floodwaters.

Railroad spokesman Andy Williams wouldn't say whether the train engineer knew or should have known about washed-out tracks mentioned in a preliminary federal report released Thursday.

"The train was operating within its authority," Williams told The Associated Press.

"The cause of the derailment is flood related," he said, declining to comment further.

The National Transportation Safety Board report cited heavy rainfall in the area 48 hours before the June 22 derailment just south of Doon, Iowa. The report said the water washed out track and flooded a tributary of the nearby Little Rock River. The report stopped short of saying the flooding caused the 32-car derailment.

Ten of the oil tank cars were breached, the report said, releasing about 230,000 gallons (871,000 liters) of tar sands oil from Canada that was headed to a Texas refinery. Last month BNSF updated its similar spill estimate, saying that 160,000 gallons (606,000 liters) had leaked.

Regarding the differing figures, safety board spokesman Keith Holloway said preliminary data "is subject to change as more information is known." He also said that it could be 12 to 18 months before his agency issues a final report that reviews the cause of the derailment.

Much of the spilled oil was contained to an area east of the tracks then recovered. Floating barriers were installed downstream to keep oil from reaching the riverfronts and polluting the water supplies of larger communities, including Sioux City and Omaha in Nebraska.

The derailment site cleanup is expected to take several months.

The federal report also said the train was moving at 48 mph (77 kph) — just below the authorized speed for that stretch.