WASHINGTON — The Defense Department is reviewing a number of military bases to find a location that can house up to 5,000 unaccompanied migrant children as the U.S. braces for a surge of people crossing the U.S.-Mexico border illegally this spring.

The Department of Health and Human Services submitted the request for space late last week, as Homeland Security leaders warned that tens of thousands of families are crossing the border each month. That flow, said Homeland Security Secretary Kirstjen Nielsen, will grow worse this spring as the weather gets better.

The Pentagon last summer approved the use of Goodfellow Air Force Base near San Angelo, Texas, for an HHS request to accommodate up to 20,000 children. Legal and environmental requirements were finalized, but HHS never came back with a formal request to actually use the base. Officials said that the extra spaced wasn’t needed, and there also were concerns that HHS didn’t have the money to construct needed housing and other support facilities at the base.

Army Lt. Col. Jamie Davis, a Pentagon spokesman, said Tuesday that since this HHS request is smaller than last year’s, the department is doing another review. It’s unclear if the Pentagon will once again propose Goodfellow as the location or if there is another military base that may already have facilities that could accommodate the smaller-sized group.

HHS Secretary Alex Azar addressed the issue of migrant children during a hearing Tuesday before the House Energy and Commerce Committee. He said HHS is asking for $1.3 billion in the 2020 fiscal year budget and the creation of a contingency fund of up to $2 billion.

"We have requested quite a lot, but at the rate we are going with the kids coming across the border, it is quite a burden financially," he said.

Associated Press writer Ricardo Alonso-Zaldivar contributed to this report.