Dario Lopez-Mills / AP An armed and masked man guards a roadblock at the entrance to the community of Cruz Quemada, near Ayutla, on Jan. 19, 2013.

Clad in sombreros and baseball caps and clutching assault rifles, shotguns and machetes, the men take defensive positions on a hillside neighborhood of the ramshackle mountain town of Tierra Colorada and gather residents from their homes. You have suffered too much at the hands of kidnappers, extortionists and drug cartels, they tell them. It is time to fight back. “If you are in favor of our community police and want to join or support us, then step forward,” says Esteban Ramos, a leader of the local militia. First the crowd is silent. Then a middle-aged man in a red t-shirt stands up and walks forward. He is followed by a young man barely out of his teens. Finally, nine men come forward with their hands raised to the applause of the crowd. A new squad has been born.

Such vigilante groups have been spreading rapidly across Mexico’s southwestern mountains this year as crime-weary residents decide to take justice into their own hands. They now claim thousands of adherents here in the state of Guerrero, where Tierra Colorada is located, and have emerged in at least seven other states. Militias made up of farmers, mechanics, shopkeepers and taxi drivers set up check points, patrol streets and drag alleged criminals into makeshift prisons. While they have handed over most detainees to state prosecutors, they have put some on public trials, shot others dead and come under fire themselves. They have also had some tense stand-offs with police and soldiers. When a militia commander was killed last month in Tierra Colorada, hundreds of vigilantes descended on it, detaining several police officers before handing them over to state officials.

(PHOTOS: Inside Mexico’s Drug War)

The militias constitute a third force in Mexico’s drug war that has been raging intensely since 2006, claiming more than 60,000 lives. There are now cartel squads of gunmen, state security forces and these groups of armed citizens. It is yet to be seen if the vigilantes will help or hinder recently inaugurated President Enrique Peña Nieto and his promise to reduce the level of violence and crime. But it is clear that they threaten the Mexican government’s monopoly over the use of force. “This could be a very unpleasant Molotov cocktail,” said Rep. Francisco Arroyo, president of the lower house of Congress. “A state that allows citizens to arm themselves to take justice into their own hands is a failed state.”

However, the vigilantes claim they have improved security. “Many of the criminals have fled town since we came in,” explains the contingent leader Ramos. “They are too scared to be committing crime with us here. We have achieved in weeks what police and soldiers could not do in years.” Ramos, 51, normally drives a taxi but has rented out his vehicle since January when he joined the militia — which he does not get paid for. Another militiaman, Ramon Diaz, grows corn and beans but has let other family members tend to the crops as he joins the struggle. “Getting back our security is payment enough,” Diaz says. The vigilantes do however enjoy plenty of free drinks and food from shopkeepers, who appear to be pleased of their presence. “We used to be scared to go out on the street because of criminals. Now we feel much safer,” said Maria Castillo, handing the militiamen cakes from her pastry shop.

Such sentiments are not shared by all however. In February, vigilantes killed a man during a shoot out in the town of Refugio. They claim he was a drug trafficker firing at them, but family members protest his innocence. This month dozens of vigilantes had a prolonged shoot-out with criminal gunmen in the town of Xaltianguis close to the Pacific resort of Acapulco. Militia men have promised they will eventually push into the slums of Acapulco, which has been hammered by drug violence and become one of the most murderous cities in the world. “We are not scared of the cartels,” says Diaz, brandishing his weapon. “They have guns but we have guns too. And we are many.”

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Riding around with the vigilantes, however, TIME found some of their procedures for ferreting out so-called criminals to be questionable, at the least. For example, the testimony to be used against one alleged extortionist was hand written onto a piece of paper. Then about a score of militiamen jumped out of their trucks and stormed into a market looking for the suspect. He was nowhere to be found.

The Mexican government has taken a mixed approach to the vigilantes. In Tierra Colorada, a bus full of state police sat on the outskirts of town drinking soda while the militia men carried out their operations. Guerrero Governor Angel Aguirre has said the groups have reduced insecurity and promised to propose a bill in the state legislature to give the militias a legal framework. Such regulation could allow them become more of a limited community police force, similar to those that exist in some villages in Guerrero under an indigenous law.

Congressmen in the Mexican capital have called for a more severe clampdown, however. In March, the Mexican army arrested 34 vigilantes in Michoacan state. They were accused of working for the notorious drug trafficker Joaquin “Chapo” Guzman (recently named Public Enemy No. 1 by the Chicago Crime Commission). Speaking from a tour of Japan on Wednesday, Peña Nieto promised to uphold the law against all the militias. “The practice of taking justice into your own hands is outside the law and my government will combat it,” he said.

Ernesto Lopez Portillo, of Mexico’s Institute for Security and Democracy, agrees that the militias need to be disarmed but says it should be done through agreement not force. “The government needs to commit to making an unprecedented effort to invest in these communities and reduce crime,” Lopez Portillo said. “We have to understand that these self defense groups are not the cause of the violence in Mexico but a consequence. They are a response to the failure of the government to administer justice and stop the growth of organized crime.”

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