A construction crew works on the U.S. side of the U.S.-Mexico border fence as seen from Tijuana last month. (Guillermo Arias/AFP/Getty Images)

Pentagon officials are considering a new request for military assistance along the southern border, a defense official said Monday, after the Department of Homeland Security asked for help housing and caring for thousands of migrants.

The latest DHS request, first reported over the weekend by journalists accompanying acting defense secretary Patrick Shanahan on a trip to the border, comes as lawmakers voice frustration about the Pentagon’s expanding role in President Trump’s border policies, including the effort to curtail a surge in migrant crossings.

A defense official, speaking on the condition of anonymity to discuss a proposal that has not yet been approved, said the request asks the Defense Department to provide or construct shelter for at least 5,000 migrants and to provide “wraparound services,” including food and other care.

Officials are examining whether the migrants would be housed in existing military facilities or whether tents or other structures would be put in place to shelter them, the official said. If the request is approved, the migrants could be taken to a single facility or multiple sites.

Additional details about the request come only days after the Pentagon announced it would shift $1.5 billion in existing military programs to fund construction of Trump’s border wall. Democratic lawmakers decried the move, saying the decision to reallocate funding without prior consultation “ignored decades of precedent and cooperation with the Congress.”

The official said the steps to house migrants, if approved, would be paid for out of previously reallocated funds. In April, Shanahan approved a Department of Health and Human Services request to identify military facilities where migrant children could be placed if necessary.

Lawmakers from both parties have voiced concerns that the military’s expanding involvement could detract from other priorities, including restoring military readiness and repairing storm damage to bases.

The military has gradually expanded its military mission along the border, where there are now more than 4,000 active-duty and National Guard troops. To help border agents deal with a crush of people seeking to cross, Pentagon leaders have also granted limited exceptions to a long-standing policy that prevents service members from coming into contact with migrants.

In a Fox News interview that aired Monday, Shanahan responded to critics of the Pentagon’s involvement in the administration’s migrant response, saying there is a “crisis at the border.”

“The commander in chief has given me a direct legal order to secure the border,” he said. “I’m securing the border.”

Pentagon officials are now attempting to chart out a two-year plan that would anticipate DHS and law enforcement needs so that the military does not have to respond to a steady stream of requests.

Dan Lamothe contributed to this report.