Attorney General Jeff Sessions directed federal prosecutors to pursue harsher charges against undocumented immigrants who commit crimes, or repeatedly cross into the U.S. illegally, and he promised to add 125 immigration judges in the next two years to address a backlog of immigration cases.

The moves are part of the administration’s efforts to deter illegal immigration and meant to target gangs and smugglers, though nonviolent migrants could also face more severe prosecutions.

In a memo issued Tuesday, Mr. Sessions instructed prosecutors to make a series of immigration offenses “higher priorities,” including transporting or harboring illegal immigrants, illegally entering or re-entering the country, or assaulting immigration-enforcement agents.

The memo also required prosecutors to consider charging some undocumented immigrants with aggravated identity theft, which carries a mandatory two-year prison term.

In remarks Tuesday to border patrol agents at the U.S.-Mexico border in Nogales, Ariz., Mr. Sessions spoke in stark terms about the threat he said illegal immigration posed.


“We mean international criminal organizations that turn cities and suburbs into warzones, that rape and kill innocent civilians,” Mr. Sessions said in his delivered remarks, referring to gangs run by illegal immigrants. “It is here, on this sliver of land, on this border, where we first take our stand.”

The passage had drawn attention because the prepared remarks released by the Justice Department had included the phrase “take our stand against this filth.” But Mr. Sessions deviated from his prepared remarks and didn’t say “filth” as he delivered his speech.

“This is a new era,” Mr. Sessions said during his speech. “This is the Trump era.”

Former prosecutors said they didn’t expect the memo to dramatically affect U.S. attorneys offices along the southern border, which already bring thousands of such cases each year. They said it could have an impact on those farther inland, which haven’t historically focused on immigration violations.


In the fiscal year that ended in September, 52% of all federal criminal prosecutions involved immigration-related offenses, according to Justice Department data analyzed by Transactional Records Access Clearinghouse at Syracuse University.

The largest number of cases—24,549—came from the Southern District of Texas, whose border with Mexico stretches from Brownsville to Laredo, Texas.

Coming to America How immigration policy has changed the U.S.

“Those cases are brought and prosecuted on a daily basis in all those border districts,” said Jeffery Vaden, who worked as a prosecutor in that office from 1999 to 2011 and is now a lawyer at Bracewell LLP in Houston.

The memo did instruct prosecutors in the border offices to develop guidelines for prosecuting “improper entry” cases, which Mr. Vaden said his former office had not prioritized as much, given the number of such violations.


“That might be a more aggressive push. If you start filing those, there will be a lot more cases to deal with,” he said.

Peter Skinner, a former federal prosecutor in the Manhattan U.S. attorney’s office who has prosecuted immigration crimes said that cases alleging unlawful rentry are easy to bring but could stretch that office’s resources if it is required to prioritize more such cases.

“If they’re all of a sudden allocating more of their time to an immigration docket, other stuff will suffer as a result,” said Mr. Skinner, who is now a partner at Boies Schiller Flexner LLP.

According to the Trump administration, its broader crackdown on illegal immigration through raids and deportations has led to a dramatic drop in illegal crossings at the border.


In February, the government reported the lowest monthly total of illegal crossings in at least five years, according to the Department of Homeland Security.

In his remarks, Mr. Sessions said the March tally showed a 72% drop from December. Border apprehensions stood at 58,431 in December, and fell to 16,600 in March, according to Customs and Border Protection data.

The memo also instructed every district to designate a “border security coordinator” by April 18, who would be responsible for overseeing immigration-related prosecutions.

Immigration advocates said they worried that the memo and tone set by the administration was describing a closer link between criminal behavior and immigration than statistics show.

“We are seeing an overemphasis on prosecuting, at the federal level, immigration, illegal entry and re-entry cases, and far less paid to criminal violations that implicate public safety,” said Gregory Chen, director of advocacy for the American Immigration Lawyers Association.

Troy Eid, a former U.S. attorney in Colorado during President George W. Bush’s administration, said Mr. Sessions was “spot-on” to focus on illegal immigrant crimes, citing data from the U.S. Sentencing Commission that found that one in every four criminals sentenced to federal prison is an unlawful immigrant who was deported but returned illegally to the U.S.

Mr. Sessions also said the agency would put in place a “streamlined hiring plan” that he said would get immigration judges on the bench at a quicker pace.

The Trump administration previously announced a boost in hiring judges as part of its budget proposal for 2018; funding must be approved by Congress.

The Obama administration had tried to hire more judges, Mr. Chen said, but that process was slowed by vetting.

—Dan Frosch and Nicole Hong contributed to this article.

Write to Aruna Viswanatha at Aruna.Viswanatha@wsj.com