The group appeared this week in Tepalcatepec, in the western state of Michoacan, in an area dominated by warring drug cartels. Tepalcatepec is the latest in a recent wave of towns where residents have set up patrols and checkpoints to fight crimes like kidnapping and extortion.
But the previous self-defense groups were made up mainly of farmers in muddy boots or sandals, armed with a mix of shotguns, single-shot rifles, old pistols and machetes.
Video footage from the town shows that the new group of vigilantes is much better armed and dressed, with assault rifles and matching, professionally-printed T-shirts that read "Community Police" on one side and "For a Free Tepalcatepec" on the other.
Many Mexicans are concerned that the "self-defense" patrols could start acting like paramilitary groups or be used by the drug gangs themselves.
"There is a very thin line between these self-defense organizations and paramilitary groups," Raul Plascencia, the head of the country's Human Rights Commission, said earlier this month.
One of the leaders of the new vigilante group, which has already set up highway checkpoints and started questioning passing motorists, said the group was made up of common citizens exercising their constitutional rights.
"We want to escape the yoke of organized crime," said the leader, who wore a blue bandanna over his face and would not give his name. "They were charging us protection payments, extortion."
He denied that the powerful cartels that operate in the area were behind the group, saying it was being funded and supported by residents.
The vigilante movement also appears to be spreading in the Pacific coast state of Guerrero, where it began in early January. The governmental rights commission said Tuesday it had sent a team of investigators to an area of Guerrero state where the movement started, and said residents expressed anger over the failure of police to combat crime.
And a new group in Coyuca, a town just west of the coastal resort of Acapulco, announced this week that they were forming their own armed self-defense group. Most previous groups had been established in isolated rural areas.
Assistant Interior Secretary Eduardo Sanchez acknowledged the dual problems—that of restoring law enforcement to lawless areas and reigning in the vigilante groups—during a news conference Tuesday.
Sanchez said the government was seeking to negotiate with the vigilante groups.
"Our task is to establish the rule of law in both senses, by guaranteeing public safety ... and channeling these self-defense groups back into appropriate channels where citizen participation can help and complement government sources," Sanchez said.
One of the biggest concerns for rights officials has been the practice of self-defense groups of detaining people they find suspicious, and holding them, sometimes for weeks at a time, in improvised jails.
The leader of the Tepalcatepec group said self-defense patrols there had already detained "several" suspects.