WASHINGTON - U.S. immigration officials deported approximately 12,000 family members and unaccompanied minors last fiscal year, far fewer than the "millions" President Donald Trump pledged to arrest months ago in frustration about rising border crossings, according to a federal report released Wednesday.

U.S. Immigration and Customs Enforcement deported 5,702 family members, a 110 percent jump from the prior year, according to its year-end report, which covers the period from Oct. 1, 2018, to Sept. 30, 2019. Officials also deported 6,351 people who crossed the U.S.-Mexico border as unaccompanied minors, a 14 percent increase. Some had arrived in the United States as long as five years ago.

The tally comes months after Trump fumed about the record influx of Central American parents and children surrendering at the U.S. border to seek asylum, thwarting his efforts to secure the U.S.-Mexico boundary and to increase arrests of immigrants convicted of serious crimes inside the United States.

Trump threatened mass arrests of families last June, though his public proclamations about the mission upended the planned roundup, known as "Operation Border Resolve." The operation originally targeted 2,100 families but caught just 18 people.

Acting ICE Director Matthew Albence acknowledged then that the publicity likely depressed the number of arrests, but said the family operation was "just the beginning."

Speaking at a news conference Wednesday in Dallas, Albence said the introduction of tighter asylum policies, and the subsequent reduction in attempted border crossings, is freeing agents to focus on arresting more criminals. It also has allowed agents to arrest more families - and minors who have turned 18 - something they believe helps to reduce crime and deter mass migration.

"We've removed more than double the family units," Albence said. "And I suspect those numbers will go up this year as well as we continue to work these cases."

Officials acknowledged in the report that the expulsions of families and unaccompanied minors were "a small fraction" of those who entered the United States during the fiscal year. More than 540,000 family members and unaccompanied minors crossed the border, and most were released into the United States, pushing the agency's docket of "non-detained" immigrants past 3.2 million.

Officials said legal limits on detaining minors make it "extremely challenging" to deport them and their families. Albence said the Trump administration's border crackdown has helped by pushing families into Mexico to await their asylum hearings. But he said Congress should change federal law to allow authorities to more quickly deport families and unaccompanied minors, and put an end to the notion that traveling with a child will make it easier for immigrants to enter the United States. Advocates for immigrants are challenging Trump's policies in court, saying families are fleeing dangerous conditions and should be allowed to claim asylum in the United States.

Overall, ICE deported more than 267,000 people last fiscal year, a 4 percent uptick from the year before and significantly lower than the peak of 400,000 annual deportations midway through President Barack Obama's administration.

Immigration arrests inside the United States - which typically target convicted criminals - hit their lowest point since Trump took office, with 143,000, down 10 percent. Arrests of convicted criminals also dropped 12 percent, to approximately 92,000.

Officials blamed the drop in arrests and fairly flat deportations on the influx of asylum seeking parents and children at the border last year, which packed immigration jails to a record high and required officials to deploy 350 immigration agents to assist the Border Patrol instead of searching for criminals.

ICE officials also have said they are having a more difficult time making arrests in the interior of the United States because so-called "sanctuary cities" are refusing to help them.

Though ICE expanded its daily average detention capacity from 33,000 to more than 50,000 a day under the Trump administration, the largest share of detainees were recent border crossers. Officials said deporting criminals remains ICE's top priority. Of the nearly 86,000 people deported from the interior of the United States last year, more than 90 percent had criminal convictions or pending charges.

Among those taken into ICE custody, the top criminal offenders were drunk drivers, followed by those with traffic violations and drug offenses. ICE officials said the agency also deported nearly 5,500 known or suspected gang members, slightly lower than fiscal 2018, while deportations of suspected terrorists rose from 42 to 58.