MISSION, Texas (AP) -- On a recent moonlit night, U.S. Border Patrol agents began rounding up eight immigrants hiding in and around a canal near the Rio Grande. A Texas state police officer soon arrived to help. Then out of the darkness emerged seven more armed men in fatigues.
Agents assumed the camouflaged crew that joined in pulling the immigrants from the canal's milky green waters was a tactical unit from the Texas Department of Public Safety. Only later did they learn that the men belonged to the Texas Militia, a group of armed private citizens that dresses like a team of elite police officers but has no law-enforcement training or authority of any kind.
The presence of armed militia members working on their own in a region known for human smuggling, drug smuggling and illegal immigration has added one more variable to an already complex and tense situation as America's border crisis escalates.
A surge of illegal immigration put renewed attention on the border this summer. About 63,000 unaccompanied child immigrants were arrested between October and July, the vast majority of them in South Texas. Some militia and self-described "patriot" groups responded with a call to seal the border.
The Aug. 6 incident in Mission ended peacefully with the immigrants arrested and the Border Patrol advising the militia members "to properly and promptly" identify themselves anytime they encounter law-enforcement officers. But the episode was unsettling enough for the Border Patrol to circulate an "issue paper" warning other agents.
Law enforcement are warning that the militia could cause chaos throughout the Rio Grande Valley, a wide area patrolled by more than 3,000 border agents, as well as hundreds of state police, game wardens and local police officers. Gov. Rick Perry is also sending as many as 1,000 National Guard reserve troops.
"How do they identify themselves? Do they have badges? How do we know who they are?" J.P. Rodriguez, a Hidalgo County Sheriff's Office spokesman, said of the militia. "If they're all just dressed in camos, it's kind of hard to distinguish whether they're law enforcement or not. ... There's a lot of potential for stuff to go wrong."
One year ago, a member of an Arizona Minuteman border-watch group was arrested for pointing a rifle at a sheriff's deputy he apparently mistook for a drug smuggler. Maricopa County Sheriff Joe Arpaio warned of "chaos if you're going to have private citizens dressed just like our deputies taking the law into their own hands."
If militia members aren't careful in their dealings with real law officers, "there could be some dead militia out there," he added.
The Border Patrol declined to comment on the encounter in Mission, referring questions to a general statement on militias released last month by U.S. Customs and Border Protection.
That statement said the agency "does not endorse or support any private group or organization from taking matters into their own hands as it could have disastrous personal and public safety consequences."
The militia members who surprised the Border Patrol that night told agents they wanted to help with the "border crisis" and that they supported the agency's efforts, according to a copy of the issue paper obtained by The Associated Press.
Emails sent to a website for the Texas Militia were not answered.
Militias in the United States trace their roots to the U.S. Constitution. They are allowed to own their guns, citing the 2nd amendment of the U.S. Constitution, and usually pass their time together training.
Less common are operations like the one at the border, where teams of militia members, who see themselves as defenders of U.S. democracy, mobilize and head into the field. Law enforcement officials have said they will respect the militia members' right to bear arms, but will be prepared to respond to calls of trespassing if militia members do not have permission to be on private property.
The spot where the arrest happened is a popular smuggling corridor where a thumb of Mexican farmland pushes a deep pocket into South Texas. The canal, an earthen channel that delivers water to the city of Mission, is about 6 feet (2 meters) deep. Immigrants who emerge from the canal have only to cross a single sorghum field to reach a road.
Barbie Rogers, founder of the Patriots Information Hotline, said at last count there were 13 such teams on the Texas border. If they are each similar in size to the one that showed up in Mission, that would be fewer than 100 people operating on the 1,255-mile (2,000-kilometer) Texas border.
Rogers uses a website and hotline to coordinate donations and supply lines to militia groups in the field. Asked how many people that amounted to, she said, "I couldn't tell you that because it could compromise their security."
She said the teams she knows keep sheriffs' offices and the Border Patrol apprised of their activity. Asked about the Texas Militia members appearing in Mission without identifying themselves, Rogers said, "They should have. I can't imagine that they didn't."
The teams, she said, try to advise the Border Patrol as soon as they spot illegal activity.
They will detain people until authorities arrive, although Rogers acknowledged they have no authority to hold anyone.
"Usually the people coming across are so scared they just sit there and wait," she said.
Follow Christopher Sherman on Twitter at https://twitter.com/chrisshermanAP