(Radio Iowa) – Investigators are still trying to determine the cause of a train derailment Thursday in Sioux City.

A Union Pacific spokesperson says about one dozen cars on a freight train derailed upright on the edge of their Sioux City yard around 6 p.m.. There were no injuries and no releases of contents from any of the rail cars.

Union Pacific crews put all cars back on the rails this morning and 28th Street will remain closed for at least a few more days because of the repair work.

Derailed cars in Sioux City. (KSCJ photo)