WASHINGTON — Department of Homeland Security Secretary Kirstjen Nielsen announced on Monday that she will be increasing the number of Central American asylum seekers who are made to wait in Mexico until they can see a U.S. immigration judge.

Nielsen also said she will be temporarily reassigning 750 Customs and Border Protection agents to "address the influx of migrants" in certain areas, as NBC News reported last week.

Daily border crossings have surpassed a 13-year high as the number of undocumented Central American migrants, mainly families with children seeking asylum, has increased in recent months.

Last week, Nielsen sent a letter to Congress urging members to fund more detention beds for migrants and to give DHS new authority to deport unaccompanied children more quickly.

On Friday, President Donald Trump threatened to seal the border if Mexico did not end illegal immigration. A senior DHS official would not rule out such a move, but qualified Trump's remarks by saying the agency would reserve the right to stop traffic over certain ports of entry temporarily.

Currently, CBP officers and agents have the authority to turn around asylum-seekers crossing in the San Diego and El Paso sectors, under a policy known as "Remain in Mexico" or Migrant Protection Protocols that requires immigrants to stay in Mexico until their court date in the U.S.

In her announcement Monday, Nielsen directed border agents to "return hundreds of additional migrants per day above current rates." It is not known how many migrants have been returned already.