SUNLAND PARK, N.M. (Reuters) - The leader of an armed militia that spent two months rounding up migrants at the U.S.-Mexico border before he was arrested on federal weapons charges was hospitalized after a jailhouse attack, his lawyer and authorities said on Wednesday.

Larry Mitchell Hopkins appears in a police booking photo taken at the Dona Ana County Detention Center in Las Cruces, New Mexico, U.S., April 20, 2019. Dona Ana County Detention Center/Handout via REUTERS.

Larry Hopkins, 69, whose group of self-styled citizen border cops drew condemnation from civil liberties advocates, suffered broken ribs in the beating by fellow inmates on Tuesday at the Dona Ana County Detention Center in Las Cruces, New Mexico, according to his attorney, Kelly O’Connell.

Hopkins was arrested on Saturday by the FBI on an outstanding warrant accusing him of being a felon in illegal possession of firearms, a charge dating back to a 2017 search of his home.

The detention facility, about 200 miles south of Albuquerque, confirmed that Hopkins was “the alleged victim” of a Tuesday night attack and said the incident was under investigation.

“Hopkins was given medical attention for non life-threatening injuries,” county spokeswoman Kelly Jameson said in an email. She later told Reuters that Hopkins had been transferred from the jail on Wednesday and turned over to the U.S. Marshals Service.

She said Hopkins was beaten by three other inmates in the jail’s television viewing room, and no weapons were found. Jameson said she had no information on what precipitated the violence.

The attack occurred the same day that Hopkins’ United Constitutional Patriots group abandoned its encampment in Sunland Park, New Mexico, where they had spent two months patrolling a 5-mile stretch of the border and said they detained thousands of migrants they caught trying to cross into the United States.

The American Civil Liberties Union last week denounced the UCP as group of “fascist” vigilantes impersonating law enforcement to essentially kidnap Central American families seeking asylum.

New Mexico Governor Michelle Lujan Grisham, a Democrat, ordered an investigation of the group. UCP members insisted they were acting at the behest of U.S. Border Patrol agents.

O’Connell, who said on Wednesday he had spoken with Hopkins by phone, questioned the jail’s ability to protect a “very high-profile” inmate, but said he did not know why Hopkins was targeted. A UCP spokesman, Jim Benvie, said he believed it was because of Hopkins’ activity at the border.

“They put him in a pod cell with a group of people, and they had just got done watching the article about the ACLU writing about him being racist, and as a result of that he was attacked,” Benvie said in a video posted online.

Hopkins was being held without bail pending a detention hearing set for Monday in Albuquerque.

Benvie said the UCP was moving to another campsite in a couple of days and would continue to support the U.S. Border Patrol, which has said it does not support private citizens acting as law enforcement.