Outraged Mexicans protesting against the presumed murder of 43 students have set ablaze the ruling party's Guerrero state headquarters and briefly held a police commander prisoner.
Riot police clashed with protesters in running street battles as black smoke billowed from the white two-story building of the Institutional Revolutionary Party (PRI) in the southern state's capital Chilpancingo.
Violent protests have erupted in Mexico since Friday, when authorities said that gang hitmen confessed to murdering the students and incinerating their bodies after corrupt police handed over the 43 young men in September in Guerrero.
The fate of the students remains a mystery. Gang suspects told investigators the 43 bodies were burned in a landfill and dumped in a river in the town of Cocula.
Some 1,000 people, led by students and the radical CETEG teachers union, marched in Chilpancingo before throwing stones and firebombs at police.
Three officers and two journalists, including a photographer working for AFP news agency, were injured after being struck by rocks, said a civil protection official.
"The assault on our building is more than an attack against this political party. It is an aggression against Guerrero's society and represents a threat to people that should not be repeated or left unpunished," the governing PRI said.
Workers fled the building, which had undergone renovations after it was torched last year by protesters angry at a controversial education reform.
Angry that two teachers were detained, Tuesday's protesters grabbed the state's deputy public security chief, Juan Jose Gatica, and held him for several hours before releasing him to a local human rights group.
Manuel Martinez, a spokesman for the families of the 43, warned that more protests would come after another disappointing meeting with the country's attorney general and interior minister.
"We are tired of the same speeches. We want the 43 [students] back alive," he told AFP after the talks in Chilpancingo's airport. "The protests will continue. We will take away the powers of the political parties."
Parents of the students, who deeply distrust the government, say they will only believe their sons are dead when they get DNA results from independent Argentine forensic experts.
Interior Minister Miguel Angel Osorio Chong told the families that the investigation into the students' disappearance remains open and the government will "step up" efforts to find them, his office said.
He also said the Inter-American Commission on Human Rights will provide technical assistance.
The feared slaughter of the trainee teachers has undermined Pena Nieto's assurances that his security strategy was bearing fruit and reducing drug-fuelled violence that has killed more than 80,000 people since 2006.