The Trump administration is moving to end an agreement limiting how long migrant children can be kept in detention, the president's latest effort to curb immigration at the Mexican border.

A court fight is almost certain to follow, challenging the attempt to hold migrant families until asylum cases are decided.

A current settlement overseen by the federal courts now requires the government to keep children in the least restrictive setting and to release them as quickly as possible, generally after 20 days in detention.

Homeland Security officials say they are adopting their own regulations that reflect the "Flores agreement," which has been in effect since 1997. They say there is no longer a need for the court involvement, which was only meant to be temporary. But the new rules would allow the government to hold families in detention much longer than 20 days.

Tightening immigration is a signature issue for President Donald Trump, aimed at restricting the movement of asylum seekers in the country and deterring more migrants from crossing the border.

The move by the administration immediately generated fresh outrage, following reports of dire conditions in detention facilities, and it is questionable whether courts will let the administration move forward with the policy.

Trump defended it, saying, "I'm the one that kept the families together."

The Mexican government expressed concern over the prospect of prolonged detention of migrant children in the U.S. In a statement from the Foreign Relations Department, Mexico said it would monitor conditions at U.S. detention centers and continue to offer consular services to any Mexican families that may be held under the new conditions. It also said that it would keep an eye on possible court challenges and that "the appropriate legal alternatives will be evaluated."

In the U.S., immigrant advocates and Democrats decried the new regulations, saying prolonged detention would traumatize immigrant children.

"The administration is seeking to codify child abuse, plain and simple," House Speaker Nancy Pelosi, D-Calif., said in a statement.

Peter Schey, a lawyer for the immigrant children in the Flores case and president of the Center for Human Rights and Constitutional Law, said if the regulations don't match the settlement in that case, "they would be in immediate material breach, if not contempt of court."

"I think all these things are now part of the 2020 campaign," Schey said.

Acting Homeland Security Secretary Kevin McAleenan said Wednesday the regulations create higher standards to govern family detention facilities. The facilities will be regularly audited, and the audits made public.

The regulations are expected to be formally published Friday and go into effect in 60 days absent legal challenges.