WASHINGTON — Citing the threat of the coronavirus to the American public, the Trump administration said on Friday it would begin rapidly sending people who illegally cross the United States borders to their home countries and would halt the processing of undocumented migrants at ports of entry.
Chad Wolf, the acting secretary of homeland security, said the United States would also close the legal entry points along the border with Mexico and Canada to tourism. American citizens, lawful permanent residents and those crossing a border to seek medical treatment or attend educational institutions would not be affected. Commercial traffic would remain open, but port officers would stop processing those without legal authority to be in the United States, including asylum seekers.
Mr. Wolf said the Centers for Disease Control and Prevention had issued the order to turn away any people who crossed the southwestern border illegally instead of taking them to a detention center where they could ask for asylum in the United States. President Trump has sought such a restrictive policy for years, but the courts have blocked it as a violation of due process.
“We’re trying to limit the amount of contact we have with these individuals,” said Mr. Wolf, adding that many migrants who cross the border often lack documents to prove their medical history. “It’s going to be very rapid.”
Under the new rule, set to take effect Saturday, Border Patrol agents will be issued biometric tools to process migrants in the field. Migrants who have a criminal history will still be detained, but agents are being directed to take others to the nearest port of entry or airfield, where they are to be returned to their home countries. Unaccompanied children will be exempt from the rule, a Customs and Border Protection official said.
Mr. Trump said this week that his administration would begin immediately turning away migrants and asylum seekers by using the authorities granted to the surgeon general. On Friday, the president made it official.
“Our nation’s top health care officials are extremely concerned about the public health consequences of mass, uncontrolled cross-border movement,” Mr. Trump said. “That would be mostly, but even beyond, but mostly during this global pandemic.”
He deputized his top health officials on Friday as de facto spokesmen for his hard-line border policy.
Alex M. Azar II, the secretary of health and human services, said that “a number of health challenges arise when illegal immigrants arrive at our northern and southern borders.”
“When held at border facilities, these migrants were spreading the virus to other migrants, to C.B.P. agents and border health care workers and even the United States population as a whole,” he said, referring to Customs and Border Protection.
When asked about Mr. Azar’s claims that the migrants were carriers of the coronavirus, a spokesman for the agency could not point to any evidence showing that that was happening. The spokesman, John Mennell, said only that “this is exactly what we are trying to prevent.”
The rule will be in effect for up to a year, or until Mr. Azar determines it is no longer necessary, according to a Department of Health and Human Services regulation published on Friday.
As of Friday evening, Mexico had confirmed 164 cases of the coronavirus, as the United States soared over 17,000. Guatemala, El Salvador and Honduras, the so-called Northern Triangle of Central America, where many migrants are from, had 37.
Migrant detention facilities have been criticized in the past for their poor conditions. Last year, many migrant children fell ill in the crowded and cramped facilities.
Whether the policy can be carried out remains to be seen.
A Border Patrol official said on Friday that agents had not received any guidance on the rule, despite it taking effect on Saturday. It was also unclear whether agents would prevent every migrant who crossed illegally from asking for asylum in the United States before immediately returning them.
Two Border Patrol officials said the understanding among agents was that they would evaluate each illegal crosser on a “case-by-case basis,” while Mr. Trump and Mr. Wolf said that anyone who crossed illegally would be immediately sent back.
Administration officials also initially said the rule would entail returning everyone who crossed the border illegally to Mexico. But the Mexican government, which was blindsided when Mr. Trump confirmed the plan this week, has since said that it would not accept all returned migrants.
“If they return people who are neither Mexican nor Central Americans, Mexico would not accept it,” said Marcelo Ebrard, Mexico’s foreign minister. Central American migrants are sent to Mexico from the United States under a different policy, one that allows them to make an asylum claim but forces them to wait in Mexico while their cases are adjudicated.
After Mr. Ebrard stated Mexico’s position in a separate briefing, Mr. Wolf said migrants from countries other than Mexico would be taken to airfields, where flights chartered by Immigration and Customs Enforcement are routinely used to deport migrants.
While the administration is already diverting asylum seekers to Guatemala, it is unclear if it is prepared to return every migrant to their home countries. Mr. Wolf said the Department of Homeland Security is currently apprehending migrants from more than 120 countries. Coordinating such transports with the government of a migrant’s home country and securing a seat on a flight would most likely require holding the migrant for at least a short period of time.
In the past, the department has been able to return migrants to Mexico by asking them if they would voluntarily go home, according to Theresa Cardinal Brown, the director of immigration and cross-border policy at the Bipartisan Policy Center. But in those cases, migrants could opt out of that process and express a need for asylum.
She said the administration’s new rule would conflict with the immigration law that allows migrants on American soil, even those who cross illegally, to start the asylum process.
“I’ve never seen this happen yet, so we have to see how this works in practice,” Ms. Brown said. “You’re faced with a conflict. A conflict of denying entry for health reasons and a right to apply for asylum.”
Zolan Kanno-Youngs reported from Washington, and Kirk Semple from Mexico City.