Three people of "very special interest" were detained in southern Texas after a Immigration and Customs Enforcement agent was shot twice in the abdomen during a stakeout, according to local reports.

"They could be witnesses, could be participants and that's what we can say at this point," Hidalgo County Sheriff Lupe Treviño told The Monitor newspaper. "We expect to make an arrest soon and things are developing very quickly."

The three detainees were taken into custody on Tuesday evening, Treviño told the newspaper. 

ICE Special Agent Kelton Harrison was in stable condition at McAllen Medical Center after being shot Tuesday during an attack and chase in nearby Hargill, according to local reports.

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Harrison was confronted when he and at least one other agent were doing surveillance in a brushy area alongside a highway, according to the newspaper. 

The attack was similar to the ambush of sheriff's deputy at the hands of suspected Mexico Gulf Cartel members during an investigation into a kidnapping, the Monitor reported. While authorities would not say whether there were any ties to the cartels, one investigator told the paper that the case Harrison and the other agent were working on dealt with a group of human smugglers and drug traffickers in Hargill.

NBC affiliate KVEO in Brownsville, Texas, reported that there were two crime scenes; officials working on the case told journalists that Harrison was shot at his house and then was followed for about five miles by the suspect to a highway intersection.

Read the KVEO report in full

Two bullet casings, probably from a 9-millimeter pistol, were found at the junction of nearby highways, The Monitor reported. FBI, ICE, local police and other officials were searching the area as Harrison's unmarked Jeep SUV -- its rear windshield and front passenger window shot through -- stood among grazing steers, the newspaper reported.

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This was the second time in the past two months that an ICE agent has been shot. An off-duty agent was shot on May 10 by a gunman along a turnpike in Miami, the newspaper reported. 

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