Trump administration officials on Friday said they will continue to push forward with a controversial policy to require at least some Central American asylum seekers to wait in Mexico while their claims are heard, but acknowledged they are moving slowly with the process. Officials said El Paso is likely to soon see the implementation of the policy the administration calls Migrant Protection Protocols, but they declined to identify other potential sites.

“I can’t tell you when it’s going to happen. I’d like it to happen sooner rather than later because as we’re reporting every day the numbers are getting larger and larger and include more and more vulnerable populations,” a senior administration official said in a media conference call on Friday, speaking on condition of anonymity. “But we have to work very closely with our partners in Mexico to make sure we get this right. So we are expanding, I would tell you likely in the next few weeks.”

Politico reported on Thursday that implementation of MPP could begin in El Paso on Friday, but officials in the conference call said such plans weren’t imminent. “I would just say obviously we’re looking at El Paso but at this point in time I’m unable to tell you when we would start at that location,” another senior official said on the call, also on the condition of anonymity. Officials declined to identify other border cities being considered for what the administration initially called the “remain in Mexico” policy.

The administration began implementing the policy on a small scale in January in the San Diego-Tijuana area. The American Civil Liberties Union and other civil rights groups have filed a lawsuit in San Francisco to challenge the policy, but no hearings have been scheduled in their request for a temporary restraining order. So far the policy has only been applied to people who come to a port of entry to apply for asylum, but administration officials said Friday the policy would be expanded to people who are apprehended by Border Patrol agents as they enter illegally at places between ports of entry.

Local officials in both U.S. and Mexico border cities have said the policy could trigger a humanitarian crisis by forcing migrants onto Mexican cities that are plagued by violence and lack the infrastructure to handle tens of thousands of people seeking asylum in the United States. Officials on the call on Friday pushed back on that accusation. “We don’t want to create a situation that furthers a crisis already existing at the border. So when we look at locations and where to implement we need to ensure there is infrastructure on both sides of the border,” one of the senior administration officials said.

But resources in Ciudad Juárez, across the border from El Paso, already are clearly strained by hundreds if not thousands of migrants who are waiting in the city for an opportunity to go to an El Paso port of entry and apply for asylum. U.S. officials last June began strictly limiting the number of migrants allowed to proceed to an El Paso port of entry, and Mexican officials in November began handing out numbers to people waiting in Ciudad Juárez to bring some order to the process. In a recent visit to Casa del Migrante, the primary migrant shelter in Ciudad Juárez, Texas Monthly saw migrants being turned away at the gates because the facility was at capacity.

Mexican officials have said they haven’t agreed to the U.S. plan but will provide humanitarian aid if asylum seekers are sent to Mexico. The Trump administration officials on Friday reinforced that position, saying MPP “is definitely a unilateral action on the part of United States government.”

Shaw Drake, an attorney for the ACLU’s Border Rights Center in El Paso, called MPP “the single largest seismic shift in border policy ever implemented along the U.S. southern border.” He said it is the latest effort by the Trump administration to interfere with the asylum process and puts tens of thousands of vulnerable people at increased risk.

“We view the MPP policy as an illegal attempt to unlawfully deny access to asylum at the U.S.-Mexico border. And any expansion of the policy only will serve just to subject more migrants to an illegal attempt by this administration to cut off access to our humanitarian legal systems,” Drake said. “We have long documented the impacts of so-called metering systems and Customs and Border Protection’s illegal rejection of asylum seekers at ports of entry across the border, and the types of violence including kidnapping, rapes, extortion, disappearances, murders faced by migrants forced to wait in Mexico due to their unlawful denial of access at ports of entry. This only foreshadows the type of dangers that await those subjected to the so-called Migrant Protection Protocols.”

In interviews at the Casa del Migrante shelter in Ciudad Juárez, migrants told Texas Monthly they had little understanding of how their asylum claims would proceed in the United States. “Nada” was the repeated answer when asked what they knew of the U.S. legal process. When a group of about 20 was asked what they had heard in their native countries about President Trump’s immigration policies, several laughed. The word muro – wall – filled the conversation. “He only talks about the wall,” one woman from Honduras said.

But as the implementation of Migrant Protection Protocols demonstrates, U.S. immigration enforcement policy is more multifaceted than a debate over barriers. The Trump administration has made clear that it views the people at Casa del Migrante and thousands of others who have fled to the U.S.-Mexico border as bent on exploiting “loopholes” in U.S. asylum laws. The administration wants them returned home. “I have faith and trust God that it’s not going to happen, especially since all I’ve been through,” a woman from Honduras told Texas Monthly at the shelter. “It’s really hard to be here. I have cried a lot and suffered from the journey.”