Inmates launched an attack that injured three staff members in a maximum-security wing at a southeast Nebraska prison where prisoners rioted last spring, the state Department of Correctional Services said.

An inmate was being escorted inside a maximum-security housing unit at the Tecumseh State Correctional Institution Monday afternoon when he struck a staff member, the department said. Three more inmates joined the attack, prompting two other staffers to subdue the inmates. The housing unit was immediately locked down.

Nebraska Correctional Services Department spokesman Andrew Nystrom said in a news release Tuesday that the three staff members were treated at a local hospital and released. None of the four inmates involved suffered any injuries, Nystrom said.

Nystrom declined to immediately answer questions about the prison's population, security, staffing and other issues. He refused to say whether the housing unit was still locked down Tuesday morning.

State officials have blamed low staffing levels and excessive overtime as factors in the rioting that beset the facility for more than 10 hours last May 10. Five inmates were charged in the riot, but no one has been charged in the killing of two sex offenders whose bodies were discovered once order was restored at the facility. Four inmates and two guards were injured in the unrest.

An investigative report released by the corrections department in late June concluded that the riot started after too many prisoners were allowed to leave their cells for medication. There were only 57 staff members at the facility to manage 1,024 inmates when the riot began, and several were working overtime, the report said.

In November, Corrections Director Scott Frakes said prison officials had completed more than a dozen of the 83 actions recommended in the corrections report and were making progress on others. The recommended steps include an analysis for prison staff, additional training and drills, and reviews of responses to prison disturbances.