US authorities have arrested an alleged member of a militia that has been stopping migrants trying to cross the US-Mexico border.
Larry Mitchell Hopkins, 69, was detained in New Mexico as a felon in possession of a weapon.
It comes just days after a video emerged of militia members detaining dozens of migrants in the desert.
The group, United Constitutional Patriots, has been condemned by civil rights groups and local officials.
“This is a dangerous felon who should not have weapons around children and families,” said New Mexico Attorney General Hector Balderas.
“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.”
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While his statement said Mr Hopkins had been arrested as a felon, it did not specify what the underlying conviction had been.
The alleged militia member is expected to appear in court on Monday.
United Constitutional Patriots, a small volunteer group, argues it is helping US Border Patrol to deal with a surge in migrants crossing America’s southern border. It is one of several militias operating in the region.
As details of this week’s latest video emerged, New Mexico governor Michelle Lujan Grisham said on Twitter that “menacing or threatening migrant families and asylum seekers is absolutely unacceptable and must cease”.
US Customs and Border Protection have previously said they are opposed to civilians patrolling the border in search of illegal crossers.