Portside

IGUALA, Mexico — Masked assailants Wednesday set fire to the city hall in Iguala in a rampage triggered by the failure of Mexican authorities to resolve the case of 43 missing student teachers.

Dozens of protesters, many wearing masks, broke away from a peaceful march of thousands of people who were demanding that the missing student teachers be returned alive.

Flinging rocks and using poles as battering rams, the protesters broke into the city hall, which was closed, and shattered windows and smashed computers. Several protesters carried Molotov cocktails, and around 1:30 p.m., acrid black smoke began billowing out of several areas of the building.

No federal police, who have taken control of this city about 100 miles southwest of Mexico City, responded to the rampage as it unfolded over the course of an hour.

No injuries were apparent.

The attack marked an escalation of protests in the Pacific Coast state of Guerrero, where tensions have been high since scores of student teachers went missing Sept. 26 after clashing with municipal police. Those clashes left six people dead and some 20 injured. Police rounded up 43 other students, but their fate is unknown.

Iguala’s mayor and security chief fled after the bloodshed amid evidence that they had been collaborating with a regional criminal gang, Guerreros Unidos, or United Warriors.

Federal authorities later found six mass graves and retrieved 23 bodies from them but have not yet determined if the bodies belong to any of the missing students, all of whom were from a rural teachers college that is a bastion of radicalism.

Earlier in the day, Attorney General Jesus Murillo Karam laid blame for the missing students on fugitive ex-Mayor Jose Luis Abarca and his wife, Maria de los Angeles Pineda Villa, who was the city’s director of social services before fleeing with her husband.

Murillo Karam said several of the 52 police officers, municipal officials and United Warriors members who’ve been detained in the case have told authorities that Abarca ordered city police to halt the students lest they interrupt a public speech by his wife, who had been seeking the mayor’s post.

Police from Iguala and the nearby town of Cocula, which Murillo Karam said was also controlled by the United Warriors, conducted the roundup of the students and turned them over to three United Warriors members, who transported them toward an outlying community, Pueblo Viejo, he said.

The arson attack on the city hall in Iguala marked the fourth time this month that protesters have burned buildings, a rising tide of violence dogging President Enrique Pena Nieto as the dramatic disappearances drag on unresolved.

On Tuesday, some 200 teachers set fire to the regional office of the leftist Party of the Democratic Revolution in the state capital, Chilpancingo. The party, which controls the state government, is reeling amid opposition calls for its governor, Angel Aguirre, to resign. The fire gutted part of the building. Protesters also overturned a car and spray-painted graffiti, including the slogan, “We want them back alive.”

Before dawn on Monday, masked protesters set fire to an office of a state social assistance program, Guerrero Cumple, in Chilpancingo, burning computers and filing cabinets and leaving a charred mess.

The most damage was caused Oct. 14, when masked protesters rampaged through state government installations in Chilpancingo, setting several buildings on fire.

The Pena Nieto government announced this week a reward of the equivalent of $111,000 for information leading to the whereabouts of any of the missing 43 students.

All of the students are male, mostly in their late teens or early 20s. Most are sons of poor farmers and want to become teachers as a way out of poverty.