(CNN) Health and Human Services Secretary Alex Azar said Tuesday that his department was performing "one of the great acts of American generosity and charity" in its care of immigrant children.

Repeatedly pressed by CNN's Wolf Blitzer on "The Situation Room" about why HHS won't allow media cameras into facilities housing children, Azar said, "We have nothing to hide about how we operate these facilities."

"It is one of the great acts of American generosity and charity, what we are doing for these unaccompanied kids who are smuggled into our country or come across illegally," Azar added.

The Trump administration has faced international outcry since it implemented a "zero tolerance" immigration policy that resulted in thousands of undocumented families separated at the border, criticism that only intensified amid a snail's pace of reunifying those families.

Physicians' groups have criticized any practice of separating children from their parents as potentially causing lifelong damage.

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