New Mexico Gov. Michelle Lujan Grisham on Friday lashed out at members of a militia group who are stopping migrants at the border, declaring "regular citizens have no authority to arrest or detain anyone."

The American Civil Liberties Union of New Mexico has demanded that Lujan Grisham and New Mexico Attorney General Hector Balderas investigate the militia organization, United Constitutional Patriots. Some of the group's members are armed.

"That migrant families might be menaced or threatened in any way, shape or form when they arrive at our border — often times after an unimaginably arduous journey — is completely unacceptable," Lujan Grisham said in an email to NBC News.

"It should go without saying that regular citizens have no authority to arrest or detain anyone," she said. "My office and our state police are coordinating with the Attorney General's Office and local police to determine what has gone on and what can be done."

Balderas warned in a statement that "these individuals should not attempt to exercise authority reserved for law enforcement," he said.

The ACLU of New Mexico raised the alarm about the arrests in a letter sent Thursday to Lujan Grisham and Balderas.

The letter said that on Tuesday members of the group arrested nearly 300 people near Sunland Park, New Mexico. The ACLU posted excerpts of the letter on its website with video that appeared to have been made by one of the militia members.

“The Trump administration’s vile racism has emboldened white nationals and fascists to flagrantly violate the law,” the ACLU said. “This has no place in our state: We cannot allow racist and armed vigilantes to kidnap and detain people seeking asylum. We urge you to immediately investigate this atrocious and unlawful conduct."

According to Reuters, the group, made up mainly of veterans, has been patrolling in the area near Sunland Park since late February. They've been posting videos almost daily of members in camouflage and armed with semi-automatic rifles holding asylum-seekers who have crossed the border until Border Patrol arrives to arrest them.

Kevin McAleenan, acting Homeland Security secretary, said in a March 27 visit to El Paso, Texas, that Border Patrol did not help from “civil society groups” in policing the border, Reuters reported.

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