Mexican police say few teachers were involved in violence at a weekend highway protest in the southern state of Oaxaca in which six people died.

Federal Police Chief Enrique Galindo blames Sunday's violence on other, unspecified "radical groups."

Galindo says the confrontation between protesting teachers and state and federal police in Nochixtlan changed radically when the other groups arrived.

He said on Radio Formula that protesters regrouped with gasoline bombs and powerful fireworks. Galindo ordered armed police to move in after they confirmed gunshots.

About 100 to 150 protesters maintained the highway blockade in Nochixtlan on Monday. No police were present. Protesters were allowing people to pass but blocking commercial traffic.