The Trump administration has started returning Mexican migrants deep into the country’s interior as part of an expanding effort to deter illegal immigration and combat the ongoing crisis at the border.

The Department of Homeland Security started running flights from Tucson, Ariz., to Guadalajara in December. Officials say the migrants being returned are all Mexican nationals from non-border Mexican states who typically have either recently illegally entered the U.S., or who had gone through the court system but were ruled to be deportable by an immigration judge.

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The plan marks a departure from past practice of releasing migrants at the border. The idea would be to make it harder for repeat offenders to try and cross the border again if they are returned hundreds of miles away. Officials say returning people closer to their hometowns is better for them as well, and allows them to receive services from the Mexican government.

DHS says it plans to run two flights a week starting at the end of January and expects to return about 250 migrants a week. Officials say the move has been requested by the Mexican government, with which the U.S. has been working for months to stem the border crisis -- which peaked in May but still concerns officials.

The policy represents the latest change to come out of an intense effort by the Trump administration to bring in regional partners on the issue.

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“This is another example of the Trump Administration working with the Government of Mexico to address the ongoing border security crisis,” DHS spokeswoman Heather Swift told Fox News. “Mexico has been a great partner in stopping illegal migration before they reach our border and in standing up the Migrant Protection Protocol which has allowed us to provide court dates to more than 55,000 individuals.”

The Migrant Protection Protocols (MPP), also known as the “Remain-in-Mexico” policy, sees migrants (from all countries south of the border) returned to Mexico to await their immigration hearings -- ending the practice of “catch-and-release” where immigrants were released into the U.S. interior to await their hearings.

The policy was expanded over the summer and was strengthened at Tucson and Del Rio sectors in recent months. Those being flown into the Mexican interior are not part of the MPP program.

“Remain-in-Mexico” has proven controversial with human rights and pro-migrant activists, who claim it can place migrants in significant danger of kidnapping or violence by returning them to the Mexican side of the border. The program is facing a legal challenge at the Ninth Circuit Court of Appeals. A ruling is expected soon.

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That regional cooperation has also produced agreements with Guatemala, El Salvador and Honduras. The agreement with Guatemala sees migrants flown into that country to claim asylum there. Acting DHS Secretary Chad Wolf on Friday said that so far 96 migrants have been flown into Guatemala, but that only one individual eventually chose to claim asylum.

Those agreements have fueled a dramatic drop in apprehensions at the border by more than 70 percent since May. In December, law enforcement apprehended or turned away 40,620 at the border, the seventh month of decline since the more than 144,000 encountered in May.