A border patrol agent shot and killed an illegal immigrant from Mexico in a remote part of Arizona on Saturday, about 30 miles north of the U.S.-Mexico border, according to Customs and Border Protection. 

Two agents were called out to a mountainous area on reports of possible undocumented migrants on Saturday evening. 

After dismounting from their horses due to the rugged terrain, they encountered three migrants and took them into custody as a fourth migrant started running downhill into a canyon. 

"One of the Border Patrol agents followed this individual and while taking him into custody discharged his firearm fatally wounding the migrant, tentatively identified as a citizen of Mexico," Customs and Border Protection said on Wednesday. 

border fence Arizona

The border fence is seen, in Yuma, Arizona, U.S., January 22, 2022.  (REUTERS/Go Nakamura)

An autopsy determined that the migrant died of multiple gunshot wounds, according to the Pima County Medical Examiner. He was tentatively identified as a citizen of Mexico. 

CBP SEES ‘SUBSTANTIAL INCREASE' IN FENTANYL SEIZURES, CONFIRMS 153,941 MIGRANT ENCOUNTERS IN JANUARY

The Arizona Department of Public Safety provided air support on Sunday morning to retrieve the migrant's remains from the rugged terrain. 

Two other migrants were also detained by agents after the shooting. They were all transported to the Douglas Border Patrol Station. 

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Border Patrol agents on horseback.  (Fox News/Bill Melugin)

The incident is under investigation by the CBP's Office of Professional Responsibility, which will present their findings to the National Use of Force Review Board. 

The Cochise County Sheriff’s Office is working with the Mexican Consulate to identify the migrant and notify his family. 

border fence Arizona

A border fence in Nogales, Arizona.  (iStock)

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There have been 643,630 migrants encountered at the southern border in the first four months of fiscal year 2022, a 126% increase over the same time frame in fiscal year 2021. 

A Border Patrol official estimated that 220,000 migrants have evaded authorities while crossing the border since October.