Washington — The acting head of the Department of Homeland Security (DHS) urged Congress on Tuesday to approve billions of dollars in funding for the government to deal with an unprecedented flow of migrants heading towards the U.S.-Mexico border, saying the surge has hurt the morale of border officials.

"Their morale is impacted. They're tired. A lot of them have gotten sick. They've been exposed to flu, chicken pox, measles, mumps — all kinds of challenges in terms of the medical care," Acting DHS Secretary Kevin McAleenan told lawmakers on the Senate Judiciary Committee. "They're spending time overnight in hospitals, instead of patrolling the border."

"This is not the kind of the work they want to be doing — not what they're trained for," he added.

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During his first congressional appearance since the U.S. brokered an agreement with Mexico to stem the flow of migration from Central America, McAleenan asked lawmakers to sign-off on a $4.5-billion Republican-sponsored bill to bolster border security along the border and provide more funds to shelters housing migrant children in U.S. custody.

Acting Department of Homeland Security Secretary Kevin McAleenan arrives to testify before the Senate Judiciary Committee on Capitol Hill in Washington, Tuesday, June 11, 2019. Pablo Martinez Monsivais / AP

DHS official have been requesting funds for months to ramp up border enforcement, while the Department of Health and Human Services (HHS), which takes care of unaccompanied migrant children after they are detained by Border Patrol, is asking for emergency funding to increase housing capacity in shelters.

Last week, citing a "tremendous strain" on the agency fueled by the flow of migrants from Central America, the department moved to shut down all educational, recreational and legal services — including ESL classes and soccer games — offered to migrant children in U.S. custody.

During Tuesday's hearing, McAleenan continued to stress what he and other administration have been saying for months: their officers at the border are overwhelmed. Last month, apprehensions at the southwestern border hit a 13-year high, with U.S. authorities detaining or turning back more than 140,000 people.

In the last 40 days alone, the secretary added during his testimony, more than 60,000 children have entered DHS custody as unaccompanied minors or part of family units.

As part of the deal reached with Mexico last week, the Mexican government agreed to station thousands of national guard members near its border with Guatemala. The U.S., meanwhile, agreed to expand a program known as that requires asylum seekers to remain in Mexico while their claims are being processed in U.S. courts.

Secretary of State Mike Pompeo on Monday hailed the agreement reached with the Mexican government, saying the "full-blown" expansion of "Remain in Mexico," official known as the Migrant Protection Protocols (MPP) program, will make a "fundamental difference" in curbing large-scale migration.