CHILPANCINGO, Mexico — On a cool evening in February, Pioquinto Damian, the head of the Chamber of Commerce here in Guerrero's capital city, was locked away in his downtown apartment, afraid to step outside.

He was convinced that the mayor had tried to kill him in an ambush just a few days before. In response, the governor had assigned him 18 heavily armed police officers as bodyguards.

A few miles outside town, hundreds of members of autodefensas — vigilante "self-defense" militias composed largely of fed-up farmworkers — were patrolling the streets of semirural suburbs with ancient rifles and shotguns, hoping to rid them of the drug cartel thugs who had terrorized them for years.

Such is the latest trouble in the heart of Guerrero, a historically unruly southwestern state that last year suffered the highest number of homicides in Mexico, and the second-highest number of kidnappings. It could also become the next state to slide deep into chaos and create major problems for President Enrique Peña Nieto as he strives to project the image of a nation returning to peace after years of cartel violence.

That image has already been tarnished by the crisis in Michoacan, Guerrero's neighbor to the north: Last month, Peña Nieto was forced to send thousands of federal troops and police into Michoacan to avert clashes between vigilante groups and the Knights Templar drug cartel. Federal authorities, working alongside the vigilantes, are now presiding over a tenuous detente, peppered with bursts of bloody retaliation from the drug gang.

Similar autodefensa groups are now active in more than half of the 81 municipalities in Guerrero, a state of 3.5 million people, according to Mexico's human rights commission. Guerrero is perhaps best known outside the country as home to the now-faded beach resort city of Acapulco, but it has suffered as much as Michoacan, if not more, from enduring poverty, weak or corrupt local governments and the deeply embedded presence of feuding cartels.

In the last few weeks, concern over the state's stability has increased with the arrival of the armed vigilantes on the outskirts of the troubled capital, and their open deliberations over whether to proceed to the center of government power.

Equally troubling is the related case of Damian, a prominent ex-politician, civic leader and vigilante ally whose SUV was attacked Jan. 28 by gunmen as he returned from a town meeting in a suburb the autodefensas had recently taken over. At the gathering, Damian openly accused the mayor of Chilpancingo, Mario Moreno Arcos, who was also in attendance, of colluding with organized criminals.

Damian's son was injured in the attack, and his 38-year-old daughter-in-law, Laura Rosas Brito, was killed.

"It hasn't had the same attention as Michoacan, but Guerrero is in a very grave situation," said Jorge Chabat, a professor at the Center for Economic Research and Teaching. If the situation worsens, Chabat said, "it could create a sense that Peña Nieto doesn't control anything."

As in Michoacan, the autodefensas sprang up here last year in an effort to beat back the drug cartels. A scathing report released by the national human rights commission in December noted that the groups were filling a power vacuum created by state and local authorities. Many residents gave testimony to the commission claiming they had been "victims of cases of collusion between authorities and criminals." In a number of cases, residents alleged that it was government authorities who were responsible for kidnappings and other serious crimes.

The vigilante movement here has largely been a rural one. At the same time, Chilpancingo — the capital city of 187,000, on the highway between Mexico City and Acapulco — had fallen under the sway of a criminal group called Los Rojos, a spinoff of the once-powerful Beltran Leyva cartel. Throughout 2013, members of Los Rojos were leaning hard on Chilpancingo businesses, perhaps imitating the methods of Michoacan's Knights Templar, which had moved beyond drug smuggling to other low-overhead opportunities in extortion and kidnapping.

In June, one Chilpancingo business leader said that closures and lack of investment were causing the economy to shed 800 jobs per month. In August, another leader said the local economy might collapse.

Damian, 61, a former federal congressman with the left-leaning Party of the Democratic Revolution, or PRD, said that he and other business leaders took their concerns to the mayor, Moreno, a member of the president's Institutional Revolutionary Party, or PRI, but that he did little to help them. Damian then began openly accusing Moreno of being a narco-alcalde, a narco-mayor.

The small communities around Chilpancingo had been suffering as well, and on Jan. 23, the autodefensas took over the security functions of a number of them, accusing local police of being either ineffective or corrupt. Damian told reporters that the business community was considering asking the vigilantes to come to the heart of the capital to "bring order to Chilpancingo." Bruno Placido, a vigilante leader, said the militias would enter the city if the residents asked them to.

The Jan. 28 public security meeting took place in El Ocotito, one of the suburbs taken over by the vigilantes. The crowd exhorted Damian to speak. Standing next to Moreno, he lambasted the mayor for failing to act.

"Do not believe what this scoundrel says!" Damian said, referring to the politician at his side. "He wanted to be on the side of the criminals, and he did it, companeros!"

The ensuing attack on Damian and his family made national headlines. Two days later, hundreds of protesters marched through the streets of Chilpancingo, demanding peace in the capital, and justice for Damian.

Government leaders responded with promises of new security measures. Guerrero Gov. Angel Aguirre promised to add 500 state police to patrols in and around Chilpancingo. The federal public security commissioner, Manuel Mondragon y Kalb, came to Guerrero and promised a more vigorous federal response, though he did not say what it would consist of. Mondragon's office did not respond to inquiries from The Times last week.

Those promises, for now, have been enough to placate the Chilpancingo business community, which has decided not to ask for the vigilantes' help. Damian said he was worried not only about crime, but about the fallout from creating armed militias, or inviting them in.