Thousands of teachers opposed to an education reform protested in southern Mexico on Monday to denounce the deaths of eight people after violent weekend clashes that police blamed on armed "radicals."
Police said they were investigating whether officers fired first or hit any victims in Sunday's clashes in the state of Oaxaca.
The radical National Education Workers Coordinator (CNTE) union led the mostly peaceful march in the state's eponymous tourist city of Oaxaca to repudiate what it termed a "massacre."
Some 15 masked protesters launched fireworks and rocks at police guarding a state education department building, prompting officers to respond with tear gas in the brief exchange. Protesters shouted "assassins" at the police.
Clara Revilla Lucas, a 50-year-old teacher who complained that her school in a remote mountain village lacks computers and books in the local indigenous language, joined the protest to denounce "the repression against our colleagues."
The demonstration came a day after six people died and more than 100 were injured when police were deployed to break up a weeklong road blockade by the CNTE in Asuncion Nochixtlan, near Oaxaca city.
It was the most violent protest in a series of CNTE demonstrations against President Enrique Pena Nieto's education reform and the recent arrest of two of its leaders.
A journalist, meanwhile, was shot dead by unknown gunmen after taking pictures of looting in the town of Juchitan and another person was killed with him, according to Oaxaca state security chief Jorge Alberto Ruiz, who told MVS radio the two murders were "linked" to the unrest.
Authorities said police and the population were attacked by unidentified groups after officers removed the demonstrator barricades in Asuncion Nochixtlan.
Mexico's federal police had initially denied that officers were armed, saying news pictures showing police with firearms were "false."
Federal police chief Enrique Galindo acknowledged later that officers used weapons after they were "ambushed" by 2,000 "radicals," some of whom were armed.
Galindo told Radio Formula, however, that "we don't know yet" who fired first and that it would be determined by an investigation. He said teachers were not involved in the shooting.
"Autopsies are being conducted" to determine if the victims were hit by police bullets, he said.
At least 55 officers were injured, including eight who had gunshot wounds. Others were burned, lost fingers to firework blasts or were hit with machetes.
Some 53 civilians were injured in the clashes and more than 20 people were arrested.
'Radicals' or 'infiltrators'?
The six dead in Asuncion Nochixtlan include two shopkeepers, a farmer, a worker, a student and a local official, Governor Gabino Cue said.
Pena Nieto said on Twitter that he "lamented" the deaths and that the attorney general's office would help local authorities investigate the violence "and punish those responsible."
He also ordered unspecified actions to resolve the conflict.
Juan Garcia, a leader of the CNTE union in the Oaxaca region, reported that 22 other people were missing.
Garcia said the violence was perpetrated by "infiltrators" and that in response the police "fired without mercy."
Garcia asked for an investigation by the Inter-American Commission on Human Rights and his union has demanded Cue's resignation.
The CNTE has staunchly opposed Pena Nieto's education reform, which requires teachers to undergo performance evaluations.
The union has also been protesting last weekend's arrest of the leader of its Section 22 in Oaxaca, Ruben Nunez, and his deputy, Francisco Villalobos. Nunez faces money laundering charges, while Villalobos has been accused of stealing textbooks.
Radical teachers have held protests against the reform in Oaxaca and the southern states of Michoacan, Guerrero and Chiapas for months.
The government says the reform seeks to improve the quality of education, but the union sees it as an attempt to fire teachers and privatise the system.
The unrest comes a decade after protests by the CNTE and other local civil organizations were marked by violence that killed around 20 people, including US cameraman Brad Will.