The day after clashes between police and members of a radical teachers' union left at least six people dead in the southern Mexican state of Oaxaca, tension is still running high and the threat of more violence is palpable.

The violence erupted on Sunday when riot police moved in to break up a road blockade near the town of Nochixtlán, about 50 miles from the state capital, also known as Oaxaca. Footage of the moment shows molotov cocktails flying as crowds run from the scene and gunfire can be heard.

The government has said six people died in the confrontation that also injured 53 civilians and 55 police officers, eight of the latter with bullet wounds. It has blamed it all on "violent groups" within the protest movement.

Speaking by phone from Oaxaca on Monday, union leader David Estrada said that the death toll has now risen to eight. He said all the victims were shot by police. He also said all of them linked to the protest movement, while the authorities have stressed there were no teachers among the dead.

Estrada was speaking as he marched with other teachers from Oaxaca city to Nochixtlán to protest against what he called a police "massacre."

"The eight dead are almost all young men and people are full of indignation," he said. "The barricades are still there and the demonstrations will continue."

An initial government statement released on Sunday afternoon had claimed the federal police were not carrying weapons, though the authorities later backtracked after the circulation of images showing riot police firing on protesters.

Police officer carrying and pointing an assault rifle during the clash in Nochixtlán. (Photo by Luis Alberto Cruz/AP Images.)

By Monday federal police chief, Enrique Galindo, was openly admitting that officers had used firearms, though he said it had yet to be determined whether police bullets killed any of the victims.

Galindo told Radio Fórmula the police had begun evicting protesting teachers from the highway peacefully early on Sunday morning within a wider major operation to remove blockades across the state.

The police chief said the tone of the operation suddenly changed around 11:30 am, when "radical groups firing weapons" and a crowd of 2,000 people "ambushed" the police, leaving some seriously injured. This, he argued, forced the officers to make a tactical retreat, call in the support of two helicopters, and bring out their guns.

"At that moment the situation changed and it was no longer a demonstration, no longer a matter of clearing the highway of citizens exercising their right to protest," Galindo said. "It was something else."

This version, however, runs counter to the time stamp of 10:30 am on photographs and videos of the federal police shooting at protesters taken by local reporter Juan Arturo Pérez. Pérez also said that he had been unable to identify gunmen within the crowd, though he heard shots fired.

Video by Juan Alberto Pérez via YouTube.

After hours of confrontation in Noxchixtlán, the police retreated towards Oaxaca city. They became engaged in several other clashes on the way, which participants allege also involved police firing weapons, as well as indiscriminately tossing tear gas.

"Two guys got shot in the legs so we retreated to look after the wounded," student Ricardo Guerrero said in a phone interview. "We tried to block them with molotov cocktails and fireworks, but these ran out with time and we just had stones."

The protests are led by teachers from the radical National Coordinator of Education Workers, or CNTE, which has refused to accept the government's sweeping education reforms that President Enrique Peña Nieto has promoted as the answer to Mexico's dismal state schools. The teachers claim they are being unfairly blamed for the failures of a system that is broken at its core. They also charge that the reforms are laying the ground for future privatization.

Periodically violent protests have been going on for years, but the tension has increased dramatically in recent weeks as the government steps up its implementation of the reforms, which include mandatory evaluations of teachers, as well as the imposition of sanctions against those who go on strike.

This weekend's clashes also come a week after the Oaxaca teachers promised revolt and began setting up roadblocks across the state in response to the arrest of local leader Rubén Núñez on money laundering charges.

Sunday's massive crackdown operation took place amid outbreaks of intense violence involving protesters in several other parts of the state.

Local reporter Elidio Ramos was shot in the head and killed in the city of Juchitán shortly after he was taking photographs of protesters while they set buses on fire, as well as of unidentified people in hoods on a looting spree.

Ten years ago radical Oaxaca teachers led a broad alliance of social groups in an uprising against then governor Ulíses Ruíz that paralyzed Oaxaca city for almost six months. It was eventually quashed by a massive federal operation that took several weeks to fully pacify the city.

President Peña Nieto took around 24 hours to respond to the violence with a series of tweets lamenting what had happened and promising support for the state authorities in their investigation of who was responsible. He also pledged progress in tackling the underlying tension.

"I have given instructions so that the necessary actions are taken, within the framework of the law, to resolve the conflict," he said in the last of five tweets.