The American Civil Liberties Union (ACLU) of New Mexico says "armed vigilantes" are detaining migrants near the U.S.-Mexico border and is calling on officials to launch a probe into the group it calls a "fascist militia."

"[W]e cannot allow racist and armed vigilantes to kidnap and detain people seeking asylum," the ACLU said in a letter sent to the New Mexico governor and attorney general.

The organization said the group that calls itself the United Constitutional Patriots detained nearly 300 people on Tuesday near Sunland Park, New Mexico, who were seeking safety in the United States.

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A live video shared early Tuesday on the group's Facebook page shows a large group of people, including children, sitting and kneeling on the ground. A voice of the woman apparently taking the video says, "I don't know if we got 'em all. But this is crazy. I don't know what to say about this other than the fact it's gotta stop."

Other videos appear to show the group's activities along the U.S.-Mexico border, and people who just crossed into the United States.

In one video shared Wednesday by Jim Benvie, the spokesman for the United Constitutional Patriots, he appears to stop a group of seven people who just crossed an area where a border fence ends. "And of course as usual, this is why we're here, guys," he says. "Because there's no Border Patrol – they're busy right now."

A Border Patrol vehicle is later seen arriving.

Jim Benvie, 43, from Minnesota, looks on near the U.S.-Mexico border wall in Anapra, New Mexico, on March 20, 2019. The militia members say they will patrol the border near Mt. Christo Rey, "Until the wall is built." Paul Ratje/AFP/Getty Images

Armed groups have long policed the U.S.-Mexico border, according to the Reuters news agency. And recently, militias have boosted their activities in states including New Mexico, The New York Times reported.

Benvie told The Times that for two months his group camped near El Paso. "We're just here to support the Border Patrol and show the public the reality of the border," he said, according to the publication.

"If these people follow our verbal commands, we hold them until Border Patrol comes," Benvie said. "Border Patrol has never asked us to stand down."

U.S. Customs and Border Protection said in a statement early Friday it "does not endorse or condone private groups or organizations that take enforcement matters into their own hands. Interference by civilians in law enforcement matters could have public safety and legal consequences for all parties involved."

"If a member of the community witnesses or suspects illegal activity, please call 911, or if related to illegal cross-border activity, call the Border Patrol tip line at 1-877-872-7435 or 1-800-BE-ALERT," it added.

The Associated Press reported that more than 700 migrants were taken into custody along the border between Wednesday and Thursday afternoons. Border Patrol's El Paso sector, which includes New Mexico and areas in West Texas, recorded more than 1,800 apprehensions on Tuesday alone, the AP reported, citing authorities.