World

Violence threatens to mar Mexico's midterm elections

  • Members of a teachers union march towards scores of police in riot gear surrounding the office of the National Electoral Institute, in Chilpancingo, Guerrero State, Mexico, Friday, June 5, 2015. The confrontation ended peacefully. Radical groups and unionized teachers have vowed to block Sunday's voting for the lower house of congress, nine governorships and hundreds of mayorships. (AP Photo/Rebecca Blackwell)

    Members of a teachers union march towards scores of police in riot gear surrounding the office of the National Electoral Institute, in Chilpancingo, Guerrero State, Mexico, Friday, June 5, 2015. The confrontation ended peacefully. Radical groups and unionized teachers have vowed to block Sunday's voting for the lower house of congress, nine governorships and hundreds of mayorships. (AP Photo/Rebecca Blackwell)  (The Associated Press)

  • Federal police surround the offices of the National Electoral Institute, during a protest by members of a teachers union in Chilpancingo, Guerrero State, Mexico, Friday, June 5, 2015. The confrontation ended peacefully. Radical groups and unionized teachers have vowed to block Sunday's voting for the lower house of congress, nine governorships and hundreds of mayorships. (AP Photo/Rebecca Blackwell)

    Federal police surround the offices of the National Electoral Institute, during a protest by members of a teachers union in Chilpancingo, Guerrero State, Mexico, Friday, June 5, 2015. The confrontation ended peacefully. Radical groups and unionized teachers have vowed to block Sunday's voting for the lower house of congress, nine governorships and hundreds of mayorships. (AP Photo/Rebecca Blackwell)  (The Associated Press)

  • Police stand guard in the pedestrian street where a small explosive was tossed at National Action Party headquarters, in Chilpancingo, Mexico, in the early morning hours of Friday, June 5, 2015. Radical groups and unionized teachers have vowed to block Sunday's voting for the lower house of congress, nine governorships and hundreds of mayorships. (AP Photo/Rebecca Blackwell)

    Police stand guard in the pedestrian street where a small explosive was tossed at National Action Party headquarters, in Chilpancingo, Mexico, in the early morning hours of Friday, June 5, 2015. Radical groups and unionized teachers have vowed to block Sunday's voting for the lower house of congress, nine governorships and hundreds of mayorships. (AP Photo/Rebecca Blackwell)  (The Associated Press)

Violence is threatening Mexico's midterm elections, with radical teachers attempting to block Sunday's voting.

The elections for Congress, governorships and mayorships have already claimed the lives of three candidates, one would-be candidate, and at least a dozen campaign workers or activists.

But unlike the years from 2010 to 2012, when the violence appeared to come largely came from drug cartels, radical movements now pose the greatest threat.

Unidentified assailants and radical teachers on Friday burned or attacked the offices of five political parties in the southern states of Chiapas and Guerrero.

There have been tense moments on Thursday and Friday as army and police forces have faced off with protesters intent on breaking into electoral offices to burn ballots.