The number of immigrants apprehended for non-criminal violations has skyrocketed in the first year of the Trump administration, even as the number of people arrested at the border for entering the U.S. illegally has dropped to its lowest level in decades.

Immigrants taken into custody on administrative grounds jumped 42 percent since President Donald Trump took office in January, according to end-of-year data released Tuesday by the Department of Homeland Security.

Immigration offenses such as entering the U.S. illegally for the first time are civil, not criminal, violations.

President Donald Trump has regularly promised to ramp up immigration enforcement, a priority that was a central plank of his election campaign. On Tuesday, Immigration and Customs Enforcement acting Director Thomas Homan lauded the increase in administrative arrests and praised his agency's officers, declaring that "the numbers show that they operate with perfection on the president's mandate."

In an apparent pointed reference to the Obama administration, Homan said that the figures "prove that ICE officers know how to prioritize without overly prescriptive mandates," adding, "I couldn't be prouder of the men and women of ICE."

The number of immigrants in the U.S. illegally who were arrested for administrative violations rose to 110,568 in fiscal 2017, up from 77,806 for the same period last year. Although fiscal 2017 includes a roughly three-month period from October through early January when Obama was still in office, the number of administrative arrests sharply increased after Trump took office.

Immigration advocacy and support groups have criticized the Trump administration for unleashing what they say is an immigration enforcement regime that makes little distinction between people who are in the U.S. illegally who have criminal charges – and, therefore, may pose a threat to the communities they're in – and those who are here with simply civil violations.

Homan, who has forcefully defended ICE and the Trump administration's immigration enforcement measures and who was last month tapped to become ICE's permanent director, pushed back on that claim Tuesday.

Of those apprehended by ICE overall, 92 percent "had criminal convictions, were an immigration fugitive or were an illegal re-entry … which is a felony," he said, adding that that figure "is pretty much perfection in the execution."

The large increase in administrative arrests, he continued, reflects the shift in priorities from the Obama administration – which had directed ICE to focus on those accused or convicted of serious crimes – to the Trump administration, which rolled back its predecessor's directives.

"When you go from 0 to 100, you're going to see a large increase," Homan said. "This president, like him or love him, is doing the right thing. People can argue all you want about priorities and policies."

The press conference seemed designed in many ways to hammer home that message – as well as the broad support that the president has from top immigration officers. Officials in suits, and a couple in uniform, lined the walls of the briefing room, and reporters were provided lengthy packets detailing the latest statistics.

The surge in administrative arrests comes after a decline in arrests of people entering the U.S. illegally at the Southwest border, which immigration authorities cite as a benchmark for illegal immigration overall.

Customs and Border Protection, which oversees enforcement at the ports and along the border, recorded 310,531 apprehensions in fiscal 2017, a nearly 24-percent drop from the previous fiscal year and the lowest total since 1971. Arrests in the four-month period between Trump's inauguration and April, in particular, dropped by 40 percent compared to the same period last year, according to CBP.