WASHINGTON — Officials at Mississippi’s largest prison routinely violated the rights of prisoners by failing to provide mental health treatment, suicide counseling and protection from violence, a “systemic failure” that led to widespread death and despair, the Justice Department said on Wednesday.

In a 59-page report about a two-year investigation, the department’s civil rights division offered a scathing assessment of conditions at the Mississippi State Penitentiary, better known as Parchman, singling out the use of solitary confinement and enforced segregation of prisoners as particularly harmful practices that contributed to the poor mental and physical health of prisoners.

Since 2019, 10 inmates have been killed at Parchman, the result of an inadequate number of staff or ill-trained employees who were unable to stop violence, properly search inmates for contraband or identify inmates who were a danger to others or themselves, the report found. In addition, a dozen Parchman inmates have taken their own lives in the last three years.

“These systemic failures result in an environment rife with weapons, drugs, gang activity, extortion and violence,” the report concluded, after investigators interviewed inmates, guards, officials and employees and examined incident reports.

The report lists endemic problems at the prison, many stemming from a chronic lack of funding to adequately staff the sprawling facility built on the site of a slave plantation. It houses 4,800 prisoners, including nonviolent offenders and inmates awaiting execution on death row.

All or most of those issues need to be remedied quickly to comply with the constitutional protections afforded inmates under the Eighth and 14th Amendments, said Kristen Clarke, the head of the civil rights division of the Justice Department.

Conditions at Parchman “have generated a violent and unsafe environment for people incarcerated” there, Ms. Clarke told reporters on Wednesday. “We are committed to taking action that will ensure the safety of all people held at Parchman and other state prison facilities. We look forward to working with state officials to institute comprehensive reform.”

In the past, such investigations have led to negotiations between the civil rights division and individual states, often resulting in a legally binding compromise agreement known as a consent decree. Ten states, including Alabama, are operating under such agreements, which are overseen by the courts.

Ms. Clarke could sue Mississippi, but she said she believed state officials would work with the department to address the problems raised in the report.

The Parchman investigation, which began in February 2020, is one of several major prison inquiries undertaken or given greater priority under Ms. Clarke, a liberal civil rights lawyer. The department is currently examining reports of abuse and neglect at prisons in Georgia and five detention facilities for juveniles in Texas.

Gov. Tate Reeves of Mississippi acknowledged the system’s shortcomings on Wednesday. Mr. Reeves, a Republican, declined to comment on the report’s conclusions, citing the possibility of a federal lawsuit against the state, but said he had helped push through incremental but important changes that demonstrated his commitment to improving conditions.

“We have made significant strides at Parchman in the last two years, everything from significantly reducing the number of inmates at Parchman, all the way to working with the legislature this year to get funding to increase the number of officers that we have,” he told reporters.

But he suggested that Washington needed to be patient with Mississippi, one of the poorest states in the country. “We know that personnel is an issue that we need to continue to improve,” he said, adding that the state intended to “do everything in our power to very quickly solve those challenges.”

But the Justice Department’s investigation said that lack of resources was not the only issue. Poor management of the complex, stemming from “nonfunctional accountability or quality assurance measures,” also contributed to the violent and squalid living conditions many inmates experienced.

Moreover, state officials for years displayed “deliberate indifference” to those conditions, contributing to an outbreak of violence at the prison that began on Dec. 31, 2019, and continued for weeks, the department reported.

“There had been widespread reports about unlivable and unsanitary conditions throughout Parchman; violent murders and suicides on the rise; staffing plummeting to dangerous levels; and mounting concerns that gangs were filling the void,” the report said.

Despite notice of these structural and administrative crises, it continued, “records show a staff that was caught off guard, utterly overwhelmed and ultimately unable to adequately and quickly respond to fighting and significant injuries in multiple buildings.”