The Pentagon confirmed it may house up to 20,000 unaccompanied migrant children on military installations as part of the Trump administration’s plan to prosecute each person caught illegally crossing the border.

The locations could include four that have already been reviewed by the Department of Health and Human Services, (HHS) or could include other military installations or tent city locations not yet named.

“HHS has requested DoD to determine its capabilities to provide up to 20,000 temporary beds for unaccompanied alien children at DoD installations,” said Pentagon spokesman Lt. Col. Jamie Davis in a statement. “While four bases (three in Texas and one in Arkansas) have been visited by HHS for possible housing, it doesn’t mean any or all children would be housed there.”

“HHS and DOD are working closely to determine the requirements and timing for support,” Davis continued. “Secretary Mattis’ guidance has been clear: that the DoD will support our federal partners.”

DoD has previously said it would be responsible for the base security; HHS would be responsible for feeding and caring for the minors.

More than 21,000 unaccompanied minors have crossed into the U.S. since January, according to statistics reported by U.S. Customs and Border Patrol.

On the Senate floor Thursday, Senate Minority Leader Chuck Schumer, D-N.Y., questioned how DoD would be able to handle the influx of children.

“The Department of Defense has been asked if it can house 20,000 unaccompanied children between now and the end of the year. How will that work? Is it even feasible? How is the administration keeping track of the families who have already been separated and what are their plans and timetable for reuniting?” Schumer asked.

On Wednesday as part of his executive order to end the administration’s policy of separating children and parents who crossed together, President Donald Trump directed Mattis to “take all legally available measures to provide to the [DHS Secretary,] upon request, any existing facilities available for the housing and care of alien families.”

Trump also directed that DoD would “construct such facilities if necessary and consistent with law. The Secretary, to the extent permitted by law, shall be responsible for reimbursement for the use of these facilities.”

Virginia Republican Rep. Rob Wittman, who chairs the panel’s seapower subcommittee, said he expects the Pentagon to quickly retrofit military facilities to accommodate families after ironing out the logistics with DHS.

“It’s a matter of getting facilities, getting them ready, making sure you have enough water there,” Wittman said. “You get families together, meet their needs, and do it quickly. If anyone can do it, the military can because they’re used to dealing on that scale.

The Pentagon is also sending 21 military attorneys to the border to help the Department of Justice move through a backlog of thousands of prosecutions of illegal immigrants being held in detention centers there.

Members of the House Armed Services Committee said they have not yet received any details from the Pentagon on the plans to house migrant children.

Rep. Adam Smith, D-Wash., the panel’s ranking member, said he has asked Defense Secretary Jim Mattis for additional information.

“Obviously the policy is just ridiculous,” Smith said. “There are far, far better ways to treat children when they cross as refugees seeking asylum than to lock them up in various places. “I’m very concerned with how we are treating these children.”

Defense News reporter Joe Gould contributed to this report.