The United States embarked on Friday on a policy of automatically rejecting asylum claims of people who cross the Mexican border illegally in a bid to deter Central American migrants and force Mexico to handle them.
The administration has long said immigration officials are drowning in asylum cases partly because people falsely claim asylum and then live in the US with work permits.
But the busy ports of entry already have long lines and waits, forcing immigration officials to tell some migrants to turn around and come back to make their claims.
Separately on Thursday, a federal appeals court in California ruled that Trump can not immediately end the Deferred Action for Childhood Arrivals (DACA) program that shields from deportation young immigrants brought to the country illegally as children.
Over 5,200 United States troops have been sent to the border to erect razor-wire fences and provide surveillance and logistical support to the National Guardsmen and Customs and Border Patrol agents already there.
In June, then-Attorney General Jeff Sessions issued an appellate decision that sharply narrowed the circumstances under which immigrants can use violence at home as ground for US asylum.
The interim final rule posted Thursday from the Justice Department and Department of Homeland Security would bar immigrants who cross the "southern border unlawfully" from "eligibility for asylum".
The issue of the country's loose asylum laws - where foreign nationals can claim that they fear for their lives in their native country and be released into the US until their day in court - has sparked debate as a caravan of 7,000 to 10,000 Central Americans heads to the U.S.
Currently, US asylum rules do not bar people who enter the country without authorisation, and the Immigration and Nationality Act, which governs the US immigration system, specifically allows people who arrive in the United States, whether or not they do so at a designated port of entry, to apply for asylum.
But directing the migrants to the official ports could create massive backups among applicants on the Mexican side of the border.
The American Civil Liberties Union, which defends constitutional rights, said that the right to request asylum must be granted to anyone entering the country.
"Asylum-seekers have been left to camp out for days and weeks on bridges at the border, when they should be guaranteed a right to enter the country for a fair hearing". Those moves have been challenged in court.
It's unclear how many people en route to the U.S.in the current caravans will even make it to the border. Several smaller groups were trailing hundreds of miles to the south; officials estimated about 7,000 in all were in the country in the caravans.
Similar caravans have gathered regularly over the years and have generally dwindled by the time they reach the southern border.