HOUSTON — Masked militias have arrived in South Texas with semi-automatic rifles and tactical gear, causing a stir not only in border communities, but also among state officials.

News of the militias has spread at a time when the border has grown more militarized in response to an influx of Central American immigrants, many of them families and children who made the crossing unaccompanied — more than 57,000 since October.

Gov. Rick Perry activated 1,000 National Guard troops last month, drawing from the Texas State Guard as well as Texas Air and Army National Guard. That activation came on top of a state Department of Public Safety border surge, bringing the state’s total monthly cost to more than $17 million.

Perry has so far said the troops do not have arrest powers, although it appears they could if authorized by the state. Immigrant advocates and some local officials oppose granting them arrest powers.

Militia members started arriving on the Texas border in recent weeks to assist as part of a deployment they called Operation Secure Our Border: Laredo Sector. The effort entails creating a training command near San Antonio and rotating groups south to patrol private ranch land on the border with the permission of ranch owners.

The early groups included Oathkeepers, Three Percenter’s Club and Patriots. Then the Minutemen announced that they, too, were deploying.

An online controversy flared after a militia member appeared on YouTube advising members to confront and intimidate those caught crossing the border illegally. There also have been tensions between militia groups, but no major clashes have been reported.

Response to the groups has been mixed.

Supporters of the militias are planning a weeklong convoy from Murrieta, Calif. — site of recent anti-immigrant protests — to the border city of McAllen, Texas. The convoy, scheduled to start Saturday, will be “stopping to support citizen border patrols along the way.”

Mike Morris, who works with Three Percenter’s, told the Los Angeles Times that several militia groups were invited to South Texas by ranchers who face regular break-ins and “incursions” by migrant groups.

“It is a dangerous situation,” he said.

Morris said there were numerous militias operating without a central command, some armed. While some groups “observe and report,” he said, others saw the need to be armed in remote areas because if a threat arises, “the Border Patrol are stretched so thin — they may not respond.”

“Some parts of the border these days, Border Patrol has pulled back and it’s not safe,” Morris said.

Local law enforcement circulated a bulletin among themselves after a group camped out near an international bridge to Mexico in Pharr, Texas.

Some sheriffs declined the militias’ assistance, while others refused to take a position on their presence.

This week, the San Antonio Express-News published photographs of militia members patrolling the border, including an image of a Border Patrol agent leaning through an armed militia member’s car window and pointing to a map. The paper reported that a militia provided the photos on condition that the paper blur members’ faces because they feared being identified by cartels and gangs.

Outraged, members of the Texas Democratic congressional delegation wrote a letter to the state’s attorney general demanding he denounce the militias and define what they can legally do.

The dozen members of the delegation said they were “deeply disturbed” by the images of “armed and masked militia groups purportedly patrolling our Texas border in response to the arrival of unaccompanied children from Central America to our state.”

They called the militias “lawless,” warned that they “perpetuate the stigma that the border is a war zone” and requested that the attorney general “clarify the jurisdiction these militia groups have to patrol alongside local law enforcement and Border Patrol agents.”

Attorney General Greg Abbott, a Republican campaigning to replace Perry as governor, dismissed the letter through a spokeswoman.

Abbott backed the National Guard deployment and the state border surge, and has demanded the federal government foot the bill.

Abbott spokeswoman Lauren Bean called the letter a “partisan political stunt” and said that instead of complaining about the militias, the Democrats “should work with their Republican colleagues to secure federal funding for the state’s border security efforts.”

