The Army’s Fort Bliss and Goodfellow Air Force Base will house detained migrants swept up in the federal government’s crackdown on illegal immigration, Defense Secretary Jim Mattis said Monday.

“That is confirmed now that that would be the two bases ― Goodfellow Air Force Base and Fort Bliss,” Mattis said during a press conference in Alaska. “But I cannot confirm the specifics on how they’ll be used.”

Mattis has said several times recently that the Pentagon is prepared to support whatever help the Department of Homeland Security and Department of Health and Human Services request. The request already has some members of Congress offering amendments to the 2019 defense bill to prohibit funds from being used to pay for any construction of temporary shelters at the bases.

Mattis defended the use of the bases.

“Providing housing shelter for those who need it is a legitimate governmental function,” Mattis said. “I recognize the political aspects of it but for us it’s a logistics support effort.”

The number of detained migrants who might be held at Bliss and Goodfellow has not been announced, but the Pentagon had said last week that it had been asked to be prepared to shelter as many as 20,000 unaccompanied children.

One defense official said on the condition of anonymity that unaccompanied children detained after crossing the U.S. border would be sheltered at one of the bases and the other base would house families of migrant detainees. Under the arrangement, the Defense Department would provide the land but the operations would be run by other agencies.

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In his remarks on Sunday, Mattis said the Pentagon has a long history of providing housing to civilians in special circumstances, such as Vietnamese refugees who fled their country after the war.

“We consider that to be a logistics function that’s quite appropriate” for the department, Mattis said Sunday.