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 yesterday.
Some 1,000 people, including students and members of the radical CETEG teachers union, had marched in the city before battling police, throwing stones and firebombs.
At least five people were injured after being hit by rocks, including three officers and two journalists, a civil protection official told AFP. One of them is a photographer working for AFP.
The office had undergone renovations after it was torched last year by protesters angry at a controversial education reform.
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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.
The crime 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.
Pena Nieto was in China for a summit on yesterday despite criticism over his decision to travel in the midst of the crisis.
Protesters besieged the airport of Guerrero's Pacific resort of Acapulco for three hours on Monday, forcing three flight cancellations, after clashing with police.
On Saturday, a group of 20 demonstrators briefly set fire to the wooden door of the National Palace in Mexico City at the end of a march that had drawn thousands of people.