Violent clashes between police and members of a radical teachers' union who had blockaded a highway in southern Mexico have left six people dead and more than 100 injured, officials said.
The activists from the National Co-ordinator of Education Workers, or CNTE, are opposed to the mandatory testing of teachers as part of education reform and are also protesting over the arrest of union leaders on money laundering and other charges.
In clashes in the southern state of Oaxaca, protesters threw stones and petrol bombs, and burned vehicles, while riot police were said to have fired on protesters. Clashes took place in several municipalities in Oaxaca, but the most violent were in Nochixtlan, north of the state capital, also called Oaxaca.
In a late-night press conference, state governor Gabino Cue, accompanied by Federal Police chief Enrique Galindo, raised the death toll from the clashes in Nochixtlan to six. They said 53 civilians, 41 federal police agents and 14 state police officers were injured. Twenty-one people were detained.
Mr Cue said all the dead were civilians, with two having ties to the CNTE union.
Earlier, Mexico's 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.
Footage showed at least one police officer firing a gun several times, though it was unclear if he was a federal or state agent.
Mr 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 continued outside Oaxaca city and in the municipalities of San Pablo Huitzo and Santiaguito, where protesters burned federal police installations.
Over the past week, unionised teachers have blockaded streets, a shopping centre and 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 in Tehuantepec.
Federal prosecutors accuse union leaders of setting up an illegal financial network to fund protests and line their own pockets. They allege the scheme operated in 2013/15, when the union effectively controlled the payroll of Oaxaca's teachers.
Following the arrest of some if its 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.