SAN DIEGO/EL PASO (Reuters) - A U.S. judge on Wednesday questioned how the government would be able to properly attend to Central American asylum seekers forced to live in Mexico while their claims are processed, on the same day the government expanded the program to El Paso.

The program is a key part of measures by U.S. President Donald Trump’s administration to curb the flow of mostly Central American migrants trying to enter the United States.

Critics say it violates U.S. law and international norms as migrants are sent back to often dangerous towns in Mexico, where it is difficult to keep track of their U.S. court dates and to find legal help.

On the second day of hearings under the program, known as Migrant Protection Protocols (MPP), Judge Jonathan Simpson at a San Diego courthouse repeatedly asked the government’s attorney how to handle cases of applicants told to wait for their U.S. court dates in Mexican border towns.

“How does the court serve them if we do not have an address?” Simpson asked, after saying he was concerned whether the government could serve notices for court appearances to migrants in Mexico.

“I don’t have the answer,” replied government attorney Robert Wetteis.

Simpson on Wednesday heard petitions from 12 migrants, with two saying they were confused over appearance orders with conflicting dates. Applicant William Melendez said he received two orders to appear, each scheduled 10 days apart, and was unclear if both were valid.

A Honduran migrant named Jorge C.N. was taken into Customs and Border Patrol custody overnight because he had been told to arrive at a port of entry for a court appearance the following day, his lawyer said.

He withheld his full name to protect his privacy.

Several other applicants did not have lawyers because they said it was hard to find attorneys to take cases in Mexico, and that even making phone calls to the United States posed a challenge.

Four more people scheduled to appear did not show up at the border port of entry, where they had been told to meet officials to escort them to court.

On Wednesday, the Department of Homeland Security said it would begin next week to send asylum seekers back from El Paso, just north of Mexico’s Ciudad Juarez, the third port of entry to do so after San Ysidro, a district across from Tijuana.

The U.S. government in a court filing on Monday said that returns had also commenced through the Calexico port of entry, over the border from Mexicali.

The three crossing points fringe Mexico’s northern border zone that has witnessed extensive bloodshed over the past decade as a main battlefield of warring drug cartels.

Texas Democratic Representative Veronica Escobar said she would stand up against the program’s expansion to El Paso.

“With this shameful policy, the administration is endangering lives, abandoning its obligation to bring forward smart solutions for our broken immigration system, and imposing on another country the task of solving our immigration challenges,” she said in a statement.

Immigration attorneys and activists said they feared the move would put further strain on the resources of Ciudad Juarez, where a surge of migrants arrived in February.

(Corrects the number of ports where the policy has been applied in paragraph 12.)