Violent clashes between police and members of a radical teachers' union, who had blockaded roads in southern Mexico, have left at least six people dead and more than 100 injured, officials said.

The teachers from the National Coordinator of Education Workers, or CNTE, are opposed to the mandatory testing of teachers as part of Mexico's sweeping education reform and are also protesting against the arrest of union leaders on money-laundering and other charges.

In Sunday's clashes in the southern state of Oaxaca, protesters threw stones and Molotov cocktails, and burned vehicles, while journalists saw riot police firing on demonstrators. Clashes took place in several municipalities in Oaxaca, but the most violent were in Nochixtlan, north of the state capital also called Oaxaca.

Officials said six people were killed in Nochixtlan while 53 civilians, 41 federal police agents and 14 state police agents were injured.

Oaxaca state Governor Gabino Cue said all the dead were civilians, with two having ties to the CNTE union. A state official had previously said a state police officer was killed but it turned out that the person was a civilian.

'Gun attacks'

Earlier on Sunday, Mexico's federal government released a statement saying 21 federal police had been wounded, three of them by gunfire, and that its agents who participated in the operation were not carrying guns.

"The attacks with guns came from people outside the blockades who fired on the population and federal police," it said.

But footage filmed by The Associated Press agency shows at least one police officer firing a gun several times, though it was unclear if he was a federal or state agent.

Late on Sunday night, Federal Police chief Enrique Galindo acknowledged that he had sent in some officers with guns after agents came under fire.

"The police obligation is to protect the population," he said.

Clashes were continuing on Sunday night outside Oaxaca city and in the municipalities of San Pablo Huitzo and Santiaguito, where protesters had burned federal police installations.

Over the past week, unionised teachers have blockaded streets, a shopping mall and even train tracks in the western state of Michoacan. They have also forced some bus lines to cancel trips to Oaxaca, which is a popular tourist destination, and blocked a highway. And in Oaxaca city, protesting teachers have set up an encampment in the city's main square.

Federal prosecutors accuse union leaders of setting up an illegal financial network to fund protests and line their own pockets. They allege that the scheme operated in 2013-2015, when the union effectively controlled the payroll of Oaxaca's teachers.

Following the arrest of some if its top leaders, the union called for a revolt against Mexico's government.
Ten years ago, the teachers started a six-month takeover of Oaxaca that did not end until police stormed the barricades.

Source: Al Jazeera and agencies