MEXICO CITY — The Mexican government announced on Friday it was sending army troops, marines and federal police to southern states to protect polling places as violence threatened the country's midterm weekend elections. The decision came after radical teachers attacked the offices of political parties in the southern state of Chiapas, burning the contents, and vowed to block the voting. The deployment is “aimed at ensuring all Mexicans can go to the polls peacefully,” Mexico's Interior Department said in a statement. It said troops would be sent particularly to southern states and Oaxaca, where many of the attacks and ballot burnings have occurred. Violence ahead of the Sunday elections for Congress, governorships and mayorships has 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 appear to pose the greatest threat. Radical teachers on Friday burned or attacked the offices of five political parties in Tuxtla Gutierrez, the capital of Chiapas. They broke into the offices, ransacked the contents — computers, paperwork and furniture — and burned it in the street. In the southern state of Guerrero, unidentified assailants tossed an explosive device at the offices of the conservative National Action Party, damaging the windows. There have been tense moments in recent days as army and police forces faced off with protesters intent on breaking into electoral offices to burn ballots, as they have done in recent days. “I think this is the worst (election violence) in a lot of ways,” said Jesus Silva-Herzog Marquez of the Monterrey Technological University. “We didn't have this level of violence even in 1994, when we had elections at the same time as the Zapatista guerrilla conflict.” The teachers have issued wildly ambitious demands, including 100 percent pay hikes and the end of a constitutionally-mandated teacher evaluation system. In the colonial city of Oaxaca, teachers have burned ballots and blocked gasoline distribution facilities. Their leaders told local media they would block elections, even if they got the pay hikes. “They are using pressure, not to get any demand met, but rather to block the elections, that is their goal,” said Raul Benitez, a security expert at Mexico's National Autonomous University. In 2010, a drug cartel assassinated a leading candidate for governor in the northern state of Tamaulipas, and also killed several mayors. In this year's elections, it is not yet clear whether the killing of a candidate in Michoacan and another on the outskirts of Mexico City were related to drug violence. Two contenders for mayorships were also killed in Guerrero, where it appears more likely that criminal gangs were involved. “I think organized crime isn't getting involved in these cases, except in Guerrero,” said Benitez, suggesting the drug cartels may be happy to see the radical movements causing disturbances that would draw police attention away from the gangs. “The more unstable Guerrero is, the better it is for the criminals,” Benitez said. Electoral officials have said they will go ahead with Sunday's elections as planned, but that they don't want to militarize the elections. — AP