The leader of a New Mexico militia group that has been seen on video detaining large groups of Central American families at the Mexican border was arrested Saturday and charged with being a felon in possession of a firearm and ammunition, investigators said.

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Larry Mitchell Hopkins, 69, a leader with the United Constitutional Patriots, which has had armed civilians posted at the southern border for months, was taken into custody by the FBI, the New Mexico Attorney General's Office said.

"(Hopkins) is a dangerous felon who should not have weapons around children and families," Attorney General Hector Balderas said in a statement. "Today's arrest by the FBI indicates clearly that the rule of law should be in the hands of trained law enforcement officials, not armed vigilantes."

An FBI spokesman told The Associated Press that no additional information would be released until after Hopkins has an initial appearance in federal court on Monday.

Videos seen widely earlier in the week show members of the militia group ordering groups, including families with small children, to sit in the dirt and wait for U.S. Border Patrol agents to arrive.

U.S. Customs and Border Protection has said it does not condone these activities.

“Interference by civilians in law enforcement matters could have public safety and legal consequences for all parties involved,” the agency said.

The Associated Press contributed to this report.