The Justice Department has opened a civil rights investigation into the conditions at four Mississippi state prisons after a wave of inmate deaths in recent weeks, federal authorities announced Wednesday. At least 15 people have died inside state facilities since late December.

The department's Civil Rights Division will determine whether the state's department of corrections adequately protects inmates as well as investigate its suicide prevention services and mental health care.

The four facilities include the Southern Mississippi Correctional Institute, the Central Mississippi Correctional Facility, the Wilkinson County Correctional Facility and the Mississippi State Penitentiary at Parchman, where most of the deaths have occurred.

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Rapper Yo Gotti and Team Roc, the charity group affiliated with Jay-Z's Roc Nation, filed a federal lawsuit against the state's department of corrections on behalf of more than two dozen inmates. The suit claims people are dying because the state "has failed to fund its prisons."

Yo Gotti, in a statement to CBS News, said he was "encouraged" by the Justice Department's announcement but said the lawsuit would be moving forward: "We're hopeful their findings will lead to statewide reforms to these facilities. However, until we receive tangible commitments to shut these prisons down and move inmates to safer facilities, we will proceed with our lawsuit."

The lawsuit claims state prisons do not provide basic necessities, such as a place to sleep. Inmates are allegedly forced to live amid flooding, overflows of raw sewage, black mold, rat infestations and lack of running water and electricity.

Last month, the Mississippi Department of Corrections said Tommy Taylor, the state's interim corrections commissioner, is working with Governor Tate Reeves "to improve prison conditions for the inmates and the employees for the safety of everyone."