US Deputy Attorney General Sally Yates. Reuters/Kevin Lamarque The Department of Justice will be phasing out its use of private prisons for federal inmates, Deputy Attorney General Sally Yates announced in a memo on Thursday.

Yates told officials that the Justice Department's goal is "reducing — and ultimately ending — our use of privately operated prisons."

She directed officials to either "substantially reduce" or decline to renew expiring contracts for private prison operators.

"They simply do not provide the same level of correctional services, programs, and resources; they do not save substantially on costs; and ... they do not maintain the same level of safety and security," Yates wrote in the memo.

The move comes in the wake of a blistering report from the Justice Department last week, which found that private prisons are more dangerous than federal Bureau of Prisons facilities — both for inmates and guards.

Private prisons — also known as "contract prisons" — first became popularized as a solution to overcrowded government-run prisons. But last week's report found substantially more safety and security incidents occurring per capita than their government-run counterparts.

In 2013, approximately 30,000 federal inmates were housed in contract prisons — roughly 15% of all federal inmates. As of December 2015, that number was about 22,000, or 12 percent. In that time, though, the federal prison population dropped from 220,000 to 197,000.

Data from 14 private prisons and 14 government-run prisons showed that the former far outpaced the latter in terms of contraband, reports of incidents, lockdowns, inmate discipline, telephone monitoring, selected grievances, urinalysis drug testing, and sexual misconduct.

The Office of the Inspector General noted in the report a series of incidents at private prisons that have raised alarm, including the death of a correctional officer at the Adams County Correctional Center in Natchez, Mississippi, in 2012, as well as riots and assault of prison staff at multiple facilities.

Private prisons have come under heightened scrutiny in recent months, particularly after a Mother Jones investigation revealed disturbing conditions for inmates and guards in Louisiana's Winn Correctional Center, after reporter Shane Bauer spent four months undercover as a prison guard.

In the memo, Yates noted that private prisons "served an important role during a difficult period," but ultimately fell short on providing services, programs, and resources.

"Now with the decline in the federal prison population, we have both the opportunity and the responsibility to do something about that," Yates told The Washington Post.

All private prisons housing federal inmates are run by one of three companies: Corrections Corporation of America; the GEO Group, Inc.; and Management and Training Corporation.

The companies' stocks tanked on Thursday after the news.

GEO, a Florida-based provider of corrections facilities, fell by as much as 30%. It was halted for volatility amid the decline. CCA fell 19%; it was also halted.