WASHINGTON — The Trump administration announced a new policy Thursday that will require asylum-seekers who enter the country illegally to return to Mexico while they await decisions on their asylum claims.

According to prepared remarks before Congress by Department of Homeland Security Secretary Kirstjen Nielsen, the U.S. has reached a deal with Mexico that will allow border agents to begin turning back immigrants who cross the U.S. southern border between legal ports of entry.

"They will have to wait for approval to come into the United States. If they are granted asylum by a U.S. judge, they will be welcomed into America. If they are not, they will be removed to their home countries," Nielsen said in her remarks.

Nielsen added that the Mexican government has committed to providing humanitarian aid for immigrants waiting to enter the United States.

Due to a backlog in U.S. immigration courts, asylum cases can take months or years to reach a decision.

The new policy is the latest strike by the Trump administration to crack down on asylum-seekers, whose applications more than doubled in 2018. And it is likely to add thousands more immigrants to cities along the U.S.-Mexico border, many already full of Central Americans sleeping on sidewalks as they await their chance to enter the United States.

Under a policy known as "metering," U.S. Customs and Border Protection has been allowing only a trickle of undocumented immigrants through legal ports of entry, while thousands wait in cities with high crime like Tijuana.

Lack of resources at border stations and metering has forced more immigrants to attempt to cross the border illegally, outside of the ports of entry, immigration advocates say. They claim that DHS is lying when they say ports of entry are at capacity and not able to process more asylum-seekers.

The Trump administration previously announced that asylum-seekers who cross the border illegally would be denied asylum, but that policy has since been temporarily halted by a federal judge who ruled that under U.S. law, all immigrants have a right to claim asylum regardless of how they entered.

The new policy to turn around asylum-seekers may also be challenged in court. Nielsen cited a section of the Immigration and Nationality Act that has previously only been applied to immigrants from Mexico, not Central Americans who make up the vast majority of asylum-seekers at the southern border.