OAXACA, Mexico — Mexican authorities and protesters on Monday traded accusations of responsibility for weekend clashes that left eight people dead and more than 100 wounded in the restive southern state of Oaxaca.

Federal Police Chief Enrique Galindo, speaking on local Radio Formula, said few teachers were involved in the violence and attributed it to other, unspecified “radical groups.”

However, the radical teachers’ union involved in the protests denied that and alleged that police infiltrators were to blame.

The clashes are the latest flashpoint in an ongoing battle for control of public education in Oaxaca, where the union is resisting government attempts to implement national education reforms passed under President Enrique Pena Nieto.

Galindo said things initially went smoothly Sunday when officers moved to reopen the highway around 7 a.m. after it had been blocked by protesters. Traffic flow resumed for about two hours following dialogue between unarmed police and demonstrators from the National Coordinator of Education Workers, or CNTE.

But later the crowd swelled to about 2,000 protesters, some of them armed with gasoline bombs and powerful fireworks, Galindo added. When police confirmed gunshots, he ordered armed police to move in.

“It was a radical change of scene,” Galindo said. “It was practically an ambush.”

Late Monday, Oaxaca state prosecutor Joaquin Carrillo said in a news conference that seven civilians died of bullet wounds, none of them teachers. One more person died of wounds he suffered while handling one of the powerful fireworks that protesters used against police.

More than 100 people were wounded before police pulled back, Galindo said, adding that “staying in Nochixtlan would have brought more serious consequences.”

At the news conference, Galindo showed photos of a police helicopter that had been hit by bullets. He said three federal police officers were still being held — apparently by townspeople or protesters — in Nochixtlan.

The CNTE, in turn, said those killed were teachers and members of other social groups that support them, adding that 20 people were missing. The union denied the presence of “radical groups” and said police had infiltrated their movement. It demanded that Oaxaca Gov. Gabino Cue resign.

“This movement is not going to stop,” said union member Juan Garcia.

Several thousand teachers and activists marched in Oaxaca city, chanting “Murderers!”

Galindo said he did not know if police had fired any of the fatal gunshots. Video filmed by The Associated Press showed at least one officer firing a gun several times, though it was unclear if he was a federal or state agent.