The death toll from clashes between police and protesting teachers in the southern Mexican state of Oaxaca rose to 10 on Monday, as the country's authorities investigated whether the police were responsible.
The police have accused an unidentified armed group of being responsible for eight of the deaths in the town of Asuncion Nochixtlan.
Two other people, including a journalist, were killed in another town by unknown gunmen.
In Mexico when teachers lawfully protest the federal police shoot them with machine guns.
They made the mistake of asking to meet @EPN
— Don Winslow (@donwinslow) June 19, 2016
Federal police chief Enrique Galindo responded to criticism that the police were heavily armed by saying that officers were deployed to remove the week long road blockade and armed police were sent after 2,000 unidentified "radicals" opened fire. None of the gunmen were teachers, he said.
The Mexican authorities opened a probe on Monday investigating whether police were responsible for the deaths, after thousands of protesters led by the CNTE teachers’ union denounced the killings as a "massacre."
Galindo said in a news conference that "who started or didn’t start [firing]" will be determined with the help of statements given to prosecutors by the relevant officers.
The recent violent unrest follows months of protests by teachers who reject President Enrique Pena Nieto's landmark education reforms which require educators to undergo performance evaluations before they can be placed in public schools.
The government says the intention of the reforms is to improve the quality of education.
But the teachers who object to the new regulations think that they victimise them and are aimed at privatising the education system instead of improving it.
In May, Mexico's Education Ministry announced 3,000 teachers would be expelled from Oxaca, Guerrero and Michoacan for missing work three days in row.
A Twitter user also wrote in May that the Department of Education froze the bank accounts of teachers the day after they went on strike.
Yesterday tens of thousands of teachers in Mexico went on strike. Today the Dept of Public Education froze their bank accounts #ParoNacional
— Scott Campbell (@incandesceinto) May 17, 2016
The CNTE is also protesting last weekend's arrest of its leader in Oaxaca, Ruben Nunez, who faces money laundering charges, and his deputy, Francisco Villalobos, who is accused of stealing textbooks.
A leader of the CNTE union, Juan Garcia, said 22 people who went missing during the protests still haven't been found.
Garcia also reported that some 53 civilians were injured in the clashes and more than 20 people were arrested.