WASHINGTON >> The Department of Homeland Security has formally requested space for up to 12,000 beds at a military base to detain families caught crossing the border illegally, the Defense Department said today.

The request seeks 2,000 beds to be up and running in the next 45 days, and the remaining space to be available on an as-needed basis, the Defense Department said in a statement.

The facility must comply with Immigration and Customs Enforcement’s family residential standards, as well as a 1997 agreement known as the Flores settlement, which governs how children are housed in immigration custody. Those standards require air conditioning, libraries, private showers, plus medical, dental and mental health facilities. Those rules also state there must be freedom of movement within the facility during the day.

The facility will be housed at a military base, but it’s not clear yet which one. Defense Secretary Jim Mattis said Monday that two bases had been identified to house migrants: Goodfellow Air Force Base near San Angelo, Texas, and Fort Bliss in El Paso, Texas, which comprises more than 1 million acres in Texas and New Mexico.

In its statement, the Defense Department said if facilities are not available, it has been asked to identify available land and construct semi-separate, soft-sided camp facilities capable of sheltering up to 4,000 people at three separate locations.

The Department of Homeland Security prefers the facilities to be built in Texas, Arizona, New Mexico or California to enable access to and supervision of the sites, the Defense Department said. Doing so also would comply with the Flores agreement’s provision that reasonable efforts be made to place minors in the geographic area where the majority are apprehended, the Defense Department said.

Two Trump administration officials told The Associated Press that the funding is being worked out. The facility will be staffed by Homeland Security officials and there will be no impact to training or military readiness, the officials said.

The request notes the space is for both men and women heads of households, said the officials, who were not authorized to release details of the request publicly and spoke on condition of anonymity.

Right now, three family detention centers — with a total of about 2,500 beds — are operating essentially at capacity.

Children generally can only be detained with their families for up to 20 days under the Flores agreement. Justice Department officials have requested the agreement be modified to allow for longer detention, a move that immigrant advocates say creates a second problem and doesn’t solve the first issue.

More than 2,300 children were separated from their families under the zero tolerance policy. At least 500 have been reunited so far. President Donald Trump last week issued an order that required families to remain together when caught at the border. A federal judge ruled Tuesday night that the administration has 30 days to reunify the remaining families and 14 days if the child is younger than 5.