Washington — Under an expansion of the controversial "Remain in Mexico" program, some asylum-seekers returned by U.S. authorities to northern Mexico will have to travel more than 340 miles by car to attend hearings in an American immigration court.

The Trump administration announced on Thursday that it has started sending asylum-seekers encountered near the border in Arizona to the Mexican city of Nogales as part of the Migrant Protection Protocols (MPP), the official name of the program.

Migrants returned to Nogales will be scheduled for court hearings at the immigration court in El Paso, Texas. Since the U.S. is not providing them transportation, these asylum-seekers will have to find a way to travel across hundreds of miles of territory and two Mexican border states to reach Ciudad Juárez, the city neighboring El Paso.

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"This choice presents enormous obstacles to asylum-seekers," Aaron Reichlin-Melnick, a policy counsel at the American Immigration Council, told CBS News. "Nogales is seven to eight hours from Ciudad Juárez and the journey for many can be dangerous, as it requires going through cartel-controlled territory."

A Department of Homeland Security spokesperson confirmed on Thursday that those returned to Mexico through Nogales, Arizona, "must provide their own transportation" to their hearings in El Paso, which are usually scheduled months apart. If they secure ground transportation, migrants would need to travel south to reach a highway that traverses a vast swath of remote areas in the Mexican border states of Sonora and Chihuahua, a trip that is about eight hours long.

The route of the eight-hour drive along the U.S.-Mexico border between Nogales and Ciudad Juárez. Google Maps/TerraMetrics

Announcing the move on Thursday, Acting Homeland Security Secretary Chad Wolf praised the Remain in Mexico program as an "effective tool" in the administration's efforts to stem the flow of migrants heading to the southern border. Over the past half a year, apprehensions along the U.S.-Mexico border have plummeted. The administration has attributed the drop to restrictive policies like the MPP program, which has required more than 56,000 asylum-seeker to wait in Mexico for the duration of their U.S. immigration proceedings.

But the policy had drawn strong criticism from advocates who point to the squalid and often dangerous living conditions many migrants face as they wait for their U.S. court hearings in Mexican border cities plagued by crime and insecurity.

Tens of thousands of asylum-seekers from Central America and other Latin American countries have been sent by the U.S. to cities like Matamoros and Nuevo Laredo, located in Tamaulipas, a Mexican border state the U.S. government warns Americans not to visit because of rampant criminal activity, including kidnappings, sexual assaults and murders.

In this October 31, 2019 photo, migrants rest at "La Roca," or The Rock shelter in Nogales, Mexico. Moises Castillo / AP

Migrants returned to Nogales will be in the state of Sonora, which the State Department designates a hub for crime, human trafficking and drug trade in its travel warning for the area. Like in many other parts of Mexico, warring cartels vie for control of the drug trade in Sonora.

Last month, six members of a Mormon community with dual American and Mexican citizenship, including three children, were ambushed and massacred in Sonora. Mexican authorities have suggested that a drug cartel was responsible for the killings.

In addition to the security concerns, Reichlin-Melnick, the immigration policy expert, said that having migrants returned to Nogales appear before a judge in El Paso further strains the resources of the immigration court in the Texas border city. According to Syracuse University's Transactional Records Access Clearinghouse (TRAC), the El Paso immigration court has been assigned more than 16,300 "Remain in Mexico" cases — the highest of any court participating in the program.

"Rather than address the fact that MPP has crippled the El Paso immigration court, the Department of Homeland Security's response is to pile on more cases," Reichlin-Melnick said.