WASHINGTON — Attorney General Jeff Sessions signaled Thursday his strong support for the federal government’s continued use of private prisons, reversing an Obama administration directive to phase out their use. Stock prices of major private prison companies rose at the news.

Sessions issued a memo replacing one issued last August by Sally Yates, the deputy attorney general at the time.

That memo, which followed a harshly critical government audit of privately run prisons, directed the federal Bureau of Prisons to begin reducing and ultimately end its reliance on contract facilities. Yates, in her announcement, said private facilities have more safety and security problems than government-run ones and were less necessary given declines in the overall federal prison population.

But Sessions, in his memo, said Yates’ directive went against longstanding Justice Department policy and practice and “impaired the Bureau’s ability to meet the future needs of the federal correctional system.” He said he was directing the BOP to “return to its previous approach.”

The federal prison population — now just under 190,000 — has been dropping due in part to changes in federal sentencing policies over the last few years. Private prisons hold about 22,100 of these inmates, or 12 percent of the total population, the Justice Department has said.

Yet the federal prison population may increase again given Sessions’ commitment to aggressive enforcement of drug and immigration laws, and his focus on combating violent crime. Thursday’s memo likely sets the stage for a more expansive rollback of criminal justice policies enacted by the Obama administration Justice Department, including directives against seeking mandatory minimum punishments for nonviolent drug offenders.

The private prison industry has been a major contributor to Republican political campaigns, particularly in recent years. As a candidate, President Donald Trump said he supports the use of private prisons, and the shares of the major companies — including Geo Group and CoreCivic Co., formerly Corrections Corporation of America — jumped after the election amid anticipation that the incoming administration would again turn to them.

“I do think we can do a lot of privatizations and private prisons. It seems to work a lot better,” Trump told MSNBC in March.

The federal government started to rely on private prisons in the late 1990s because of overcrowding. Many of the federal prison inmates in private facilities are foreign nationals who are being held on immigration offenses. The Yates policy did not extend to prisons used by Immigration and Customs Enforcement, which hold tens of thousands of immigrants awaiting deportation.

Immigration and human rights advocates have long complained about conditions in privately run prisons. An inspector general audit from last August said problems at private prisons in recent years included property damage, injuries and the death of a corrections officer.