"The Trump administration has been harshly criticized by Democrats for separating children from "parents", who are often adults posing as family", in order to detain them past the 20 day maximum.

The Trump administration claims the move closes a loophole in the immigration system created by the Flores agreement, which prohibited children from being kept in detention for more than 20 days.

New regulations to be announced would be "a pathway to ensure the humane detention of families while satisfying the goals" of the Flores Settlement, DHS said.

What does the new regulation do?

The Flores agreement was put into place during the Clinton administration; the Trump administration is now formally trying to replace it.

Castro questioned the safety of family detention in his statement. Once the rule takes effect, officials said, they hope to complete migrants' initial immigration proceedings within two months, which is triple the time children are held now. "We must listen to the experts and uphold Flores to protect the rights, dignity, and humanity of children".

Speaker of the House Nancy Pelosi also cited pediatricians, saying in a statement that "the Administration is seeking to codify child abuse, plain and simple".

The American Academy of Pediatrics has repeatedly said detention is not suitable for children, who may suffer numerous negative physical and emotional symptoms.

The announcement may come as soon as Wednesday, ABC said.

"The new rule will protect children by reducing incentives for adults, including human smugglers, to exploit minors in the unsafe journey to our border", McAleenan said. Advocates have vowed to challenge the rule in court, which will put the change in front of U.S. District Judge Dolly Gee, who denied the administration's request a year ago to extend family detentions. More than 2,900 children were separated from their parents as a result.

The Flores agreement sets standards of care for children who cross the border alone as well as with families. Countless more sleeping on concrete floors under tinfoil blankets. Homeland Security officials say they are adopting regulations that reflect the agreement and there is no longer a need for court involvement, which was only meant to be temporary. "The cruelty will only get worse-until we end it", O'Rourke wrote.

The new rule would take effect 60 days from this Friday.

"This single ruling has substantially caused, and continued to fuel, the current family unit crisis and the unprecedented flow of Central American families and minors illegally crossing our borders, until today", said said Kevin McAleenan, acting secretary of the Department of Homeland Security. A pending legal challenge by the ACLU claims those ongoing separations are often based on flimsy evidence or minor crimes like traffic violations.

Holly Cooper, co-director of the immigration law clinic at University of California, Davis and a lawyer in the Flores case, said attorneys haven't seen the final rule and will have a week to brief a federal judge, who will weigh whether they are consistent with the settlement. Senate Minority Leader Chuck Schumer urged courts to block the rule.

McAleenan said that in the 10 months to July, some 475,000 people in family units crossed the border illegally from Mexico, aiming to stay in the United States.