(Adds Mexican reaction)
By Daniel Trotta and Richard Cowan
NEW YORK/WASHINGTON, July 15 (Reuters) - The Trump administration on Monday moved to bar almost all immigrants from applying for asylum at the country's southern border, requiring them to first pursue safe haven in a third country through which they had traveled on the way to the United States.
The Department of Homeland Security, in a statement issued with the Department of Justice, said the interim rule would set a "new bar" for immigrants "by placing further restrictions or limitations on eligibility for aliens who seek asylum in the United States."
The American Civil Liberties Union called the new rule "patently unlawful" and vowed to file a lawsuit.
The rule would make it all but impossible for applicants seeking protection from persecution unless they first apply for asylum in "third country" such as Mexico or Guatemala, through which they traveled en route to the United States.
It was just short of a "nuclear option, close to something like shutting down the border," said Jessica Vaughan from the Center for Immigration Studies, which supports increased immigration restrictions.
The change would also place an even higher burden on Mexico, which has been somewhat cooperative with U.S. efforts to slow Central American immigration.
Mexico pushed back on Monday, saying asylum-seekers rejected by the United States should have to go back to their home countries, not Mexico.
Mexican Foreign Minister Marcel Ebrard said the new U.S. rule would not unilaterally convert Mexico into a designated "safe third country," a status that would oblige it to offer asylum to those who entered its territory en route to the United States.
Guatemala, which both sends migrants the United States and receives Hondurans and Salvadorans passing through, said on Sunday it would postpone President Jimmy Morales' visit to Washington to discuss Guatemala's potential designation as a "safe third country" for asylum seekers, stressing it had no plans to sign such an agreement.
The proposed changes, set to become official on Tuesday, represent the latest effort by the Trump administration to crack down on immigration, the signature issue that helped propel Trump to the White House in the 2016 election and one already figuring prominently in the 2020 campaign.
Trump on Monday declared "very successful" what he had billed as a sweeping operation to arrest undocumented immigrants this past weekend. U.S. authorities launched small-scale operations aimed at about 2,000 recently arrived families in about 10 cities.
The operations come as the Trump administration faces criticism for housing immigrants in overcrowded, unsanitary conditions, and there are concerns about migrant children being separated from adults by U.S. authorities.
While Democratic politicians have sought to portray the Trump policies as inhumane, the president's supporters are certain to be pleased at another gesture making good on campaign promises to sharply curtain immigration.
U.S. Representative Doug Collins, the senior Republican on the House Judiciary Committee, said it "helps return integrity to the asylum system by focusing resources on those most at risk of persecution."
The Trump administration wants to stem a flow of asylum seekers arriving at the U.S.-Mexican border, saying U.S. capacity to process asylum claims has been overwhelmed due to an influx of people from Guatemala, Honduras and El Salvador but also increasingly from Cuba and countries as far away as Africa.
Although the three Central American countries suffer from poverty, gang violence and domestic abuse, U.S. Attorney General William Barr said many asylum claims from the three were "meritless."
The administration says that despite doubling the number of immigration judges since 2010, more than 900,000 cases are pending before U.S. immigration courts, a 13% increase since October 2018, when the number of cases had more than doubled over the previous five years. Nearly half the pending cases are asylum applications.
Acting Homeland Security Secretary Kevin McAleenan said Monday's initiative would "help reduce a major 'pull' factor driving irregular migration to the United States."
The administration's action was immediately challenged by rights groups such as the ACLU and others who questioned its legality.
The Center for American Progress called the interim rule "blatantly illegal," saying the law allows people who pass through a third country to seek asylum except in two cases that do not apply.
"The interim regulation violates the clear language of the law in several respects," Stephen Legomsky, a former chief counsel of the U.S. Citizenship and Immigration Services, told Reuters in an email.
In January Trump required many asylum-seekers to wait out their cases in Mexico, known as the "Remain in Mexico" policy or the Migrant Protection Protocols (MPP), with nearly 20,000 people sent back so far. It was not immediately clear how the new rule would affect MPP. (Reporting by Richard Cowan and Susan Heavey in Washington and Mica Rosenberg in New York; Writing by Daniel Trotta; Editing by Mohammad Zargham, Rosalba O'Brien and Tom Brown)
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