Ninety-four percent of the immigrants in the federal prison system are illegals — or 19 percent of all those under federal custody — at a total annual taxpayer cost of $1.87 billion, the Department of Homeland Security said.
According to a report mandated by President Donald Trump's immigration executive order signed in January, of the 37,557 confirmed immigrants in the federal prison system, 35,334 are in the United States illegally.
Homeland Security released the figures Thursday.
The federal prison system has a total of 185,507 inmates, 19 percent of whom are confirmed illegal immigrants, according to the report.
The $1.87 billion cost is based on 2014 estimates.
In addition, DHS noted that 58,766 federal inmates are "known or suspected" to be illegal.
Overall, the report found that more than one-in-five of all persons in custody under the Federal Bureau of Prisons were foreign born, and that 94 percent of confirmed aliens in custody were illegals.
"The American people deserve a lawful system of immigration that serves the national interest," Attorney General Sessions said in releasing the data. "But at the border and in communities across America, our citizens are being victimized by illegal aliens who commit crimes.
"Nearly 95 percent of confirmed aliens in our federal prisons are here illegally.
"We know based on sentencing data that non-citizens commit a substantially disproportionate number of drug-related offenses, which contributes to our national drug abuse crisis," Sessions said.
"The simple fact is that any offense committed by a criminal alien is ultimately preventable," he added. "One victim is too many."
Sessions called on Congress to enact President Trump's "immigration reform agenda so that we start welcoming the best and brightest while turning away drug dealers, gang members, and other criminals."