MEXICO CITY—Six protesters were killed and dozens of protesters and police were injured Sunday in clashes in southern Mexico when security forces cleared roads being blocked by members of a teachers’ group, Oaxaca state authorities said.

The clashes occurred as state and federal police sought to unblock a highway in southern Oaxaca state which the CNTE, a dissident faction of the national teachers union, had blocked to protest the arrests last week of several of the group’s leaders.

...