Mexicans furious at the presumed massacre of 43 students torched the ruling party's Guerrero state headquarters and briefly took a police commander prisoner as growing protests rocked President Enrique Pena Nieto's government.

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 authorities said Friday 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.

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, 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 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.

- More protests loom -

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 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.

- Pena Nieto abroad -

The feared slaughter of the trainee teachers has undermined Pena Nieto's assurances that his security strategy was bearing fruit and reducing drug-fueled violence that has killed more than 80,000 people since 2006.

The crime has also hurt his efforts to shift Mexico's narrative away from drug cartel mayhem and toward economic and political reforms that have won international acclaim.

Pena Nieto was in China for a summit on Tuesday despite criticism over his decision to travel in the midst of the escalating crisis. He will then travel to Australia for a meeting of Group of 20 economic powers and return Saturday.

The students vanished on September 26 after police shot their buses in Iguala, killing six people, and delivered the 43 to the Guerreros Unidos drug gang, authorities say.

Iguala's mayor ordered the attack over fears the students would interrupt a speech by his politically-ambitious wife, prosecutors say.

The students were in Iguala to raise funds but had commandeered four buses to return home.

Gang suspects told investigators the 43 bodies were burned in a landfill and dumped in a river in the town of Cocula.

The Argentine forensic experts delivered Tuesday their first results on 39 bodies found in mass graves near Iguala in October, saying 24 of them were not the students and that the rest were still being analyzed.

The forensic team said it had also participated in the recovery of the Cocula remains, but no identification has been made yet.

The government has asked an Austrian university to help with the charred remains.