Washington — The second-highest ranking official at Customs and Border Protection (CBP) said he's confident in the data his agency has publicly disclosed about the deaths of migrant children in U.S. custody. The issue sparked an uproar among Democrats and immigration advocates after it was revealed that six children have died in U.S. custody, or shortly after being released, in the past eight months.

"I'm very confident in the data that CBP has reported with respect to deaths in CBP custody," Deputy CBP Commissioner Robert Perez told CBS News during in an exclusive interview Thursday.

Pressed on whether the American public and Congress could expect to learn about other deaths that were not immediately publicized — like the September death of 10-year-old Darlyn Valle, who was in the custody of the Department of Health and Human Services (HHS) — Perez said his agency, which oversees the Border Patrol officers who first encounter migrants near the U.S.-Mexico border, is committed to an "unprecedented degree of transparency."

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He vowed to continue CBP's practice of reporting deaths of migrants in the agency's custody to congressional committees and the public.

Five Guatemalan children apprehended by U.S. authorities near the southern border have died since December, three of whom were in CBP custody and one who died shortly after being released by the agency. On Wednesday, CBS News was the first to report that Darlyn, a native of El Salvador who had a debilitating heart condition, died in government custody last year. Democratic Texas Rep. Joaquin Castro accused the Trump administration of covering up the death, which had not been previously disclosed.

Perez said a "humanitarian crisis" near the southern border, fueled by an unprecedented surge of migrant families and unaccompanied children from Central America journeying north, is "overwhelming" government detention and housing facilities and making it more difficult for his agency to take care of "vulnerable populations," like the children who have died.

"We're still making nearly 70 trips a day to the hospital across the entirety of the border because of the medical conditions that we're encountering," Perez added.

He said the resources of HHS, which typically takes in migrant children within three days of their detention by Border Patrol, are also been strained by the large-scale migration from Guatemala, El Salvador and Honduras — a region known as the "Northern Triangle" which has been plagued by widespread poverty, chronic violence and crop failures due to climate change.

Asked why Carlos Hernandez Vásquez — the latest migrant child to die — remained in CBP custody for a week before passing away and not transferred to HHS within 72 hours, Perez signaled that there's not enough funding from Congress to expand detention and bed space for migrants.

Echoing comments by Homeland Security Secretary Kevin McAleenan on Capitol Hill this week, Perez said that unless Congress approves more funding to deal with the flow of migrant families heading toward the border and changes the "legal framework" around limits on family detention, it will be difficult for his officials to prevent more deaths of migrant children in U.S. custody.

He noted that his agency is a law enforcement body and not supposed to be taking care of young children and families, especially if they are sick.

"We're not designed to take care of children, but we do it. Heartfelt and true. Every day, with every bit of will and ability that we have. And they do it exceptionally well," he added.

But without the funding and changes in immigration law that the Trump administration is requesting, Perez reiterated his officers will continue to face a daunting task at the border.

"Criminal organizations are exploiting this situation, they're exploiting the vulnerabilities in our laws, and it is costing all of us to an unprecedented level. And worst yet — most tragically — it should never be at the cost of anyone's life," he said.