The Trump administration's "zero tolerance" policy is deterring Central American migrants from traveling to the U.S., the Department of Homeland Security argued Thursday. The department cited an 18 percent drop between May and June of illegal immigrants who were either apprehended while crossing illegally or turned away as inadmissible at the southwest border.

"Following the implementation of the administration’s zero-tolerance policy, the June 2018 Southwest Border Migration numbers declined by 18 percent when compared to the previous month," DHS press secretary Tyler Q. Houlton said in a statement issued Thursday afternoon.

Newly released data from U.S. Customs and Border Protection shows 42,565 people were apprehended or deemed inadmissible in the month of June.

[Also read: 'Congress must act' to slow rising border apprehensions: DHS]

The report marked the first time since February that that figure has dropped below 50,000. In May, just under 52,000 migrants were either turned away at border stations or taken into custody by Border Patrol agents and CBP officers.

The Trump administration rolled out a zero tolerance policy in April to say it would be prosecuting all illegal entrants, including first-time offenders who were traveling with minors.

Following a national outcry, President Trump issued an executive order June 20 ordering families not to be separated. CBP Commissioner Kevin McAleenan directed his 60,000 personnel not to prosecute the majority of adults if it meant separating families, thus suspending the zero tolerance policy in mid-to-late June.

McAleenan told reporters in McAllen, Texas, last week that he expected the June numbers to be down as a result of agents increased focus on border enforcement, though he did not specify what additional measures were being taken.

However, last month, following the release of the May figures, Houlton had said it would take "many months" before border officials would be able to get a hold of the spiking numbers, which represented the highest-record levels since President Trump took office a year and a half ago.

"These numbers show that while the Trump administration is restoring the rule of law, it will take a sustained effort and continuous commitment of resources over many months to disrupt cartels, smugglers, and nefarious actors," Houlton said in a statement released one month ago. "We are taking action and will be referring and then prosecuting 100 percent of illegal border crossers, we are building the first new border wall in a decade, and we have deployed the National Guard to the border."