Two inmates have been killed during a disturbance at Tecumseh State Correctional Institution in southeast Nebraska.No details have been released about how the inmates died.The prison was placed on lockdown for roughly three hours on Thursday after inmates in a housing unit refused to return to their cells and a fire was started in a courtyard.Officials say about 40 inmates in a unit with 128 prisoners were involved.Prison spokeswoman Dawn-Renee Smith says the lockdown began around 2:45 p.m. and lasted until about 5:30 p.m.No prison employees were injured.In a statement posted on Facebook, Gov. Pete Ricketts said the incident was "swiftly resolved and public safety was never at risk."The Associated Press reports: