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Luis Alberto Cruz Hernandez, Associated Press
Riot police carry away an injured officer as they battle with protesting teachers who were blocking a federal highway in the state of Oaxaca, near the town of Nochixtlan, Mexico, Sunday, June 19, 2016. The teachers are protesting against plans to overhaul the country's education system which include federally mandated teacher evaluations.

OAXACA, Mexico — Union and state officials say violent clashes between police and unionized teachers who are blockading roads and burning vehicles in southern Mexico have left four people dead.

The radical union is opposed to the mandatory testing of teachers as part of the government's sweeping education reform and is also protesting the arrest of union leaders on money laundering and other charges.

On Sunday, an Associated Press journalist saw riot police firing on protesters in municipality of Nochixtlan in the state of Oaxaca, in an attempt to dislodge them.

Isabel Garcia, a member of the union's political commission, said three people supporting the protests were killed. And a state official, who was not authorized to speak to the press and requested anonymity, said a Oaxaca state police officer was killed.