Protesters angry at the alleged massacre of 43 Mexican students set fire Tuesday to the ruling party's regional headquarters in the southern state of Guerrero in a new demonstration over the crime.
Riot police clashed with protesters in running street battles as black smoke billowed from the two-story white building of the Institutional Revolutionary Party (PRI) in the state capital Chilpancingo.
Some 1,000 people, including students and members of the radical CETEG teachers union, marched in the city armed with sticks and many threw stones at the police, who threw projectiles back at them.
At least three people were injured, including two journalists, a civil protection official told AFP. One of them is a photographer working for AFP.
The building had been renovated after it was torched last year by protesters angry at a controversial education reform.
Violent protests have erupted in Mexico since authorities said Friday that gang hitmen in league with corrupt police confessed to murdering the 43 students and incinerating their bodies in September.
The crime has outraged Mexicans and turned into a crisis for President Enrique Pena Nieto, who was in China for a summit on Tuesday.
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.
Authorities say gang-linked police shot at busloads of students in the Guerrero city of Iguala on September 26, in a night of violence that left six people dead.
The police then handed the 43 abducted students to the Guerreros Unidos drug gang, prosecutors say.
Authorities say Iguala's mayor ordered police to confront the students over fears they would interrupt a speech by his wife, who aspired to succeed him.
The students had traveled to Iguala to raise funds but hijacked four buses to return home, a common practice among the young men from the college known for its radical left-wing politics.
Officials stopped short of declaring the students dead, stressing they were waiting for DNA results.
Parents of the missing students, who deeply distrust the government, say they will only believe their sons are dead once they get independent DNA test results.
Pena Nieto was in China for an Asia-Pacific Economic Cooperation (APEC) summit and a state visit despite criticism over his decision to travel in the midst of the crisis.