OAXACA DE JUAREZ, Mexico (AP) – Striking teachers, some armed with machetes and guns, hijacked and burned buses and blocked highways Thursday in their month-long battle with the government of the Mexican state of Oaxaca.

The increasingly violent clashes threatened to last through Mexico’s July 2 presidential election and potentially disrupt voting in the region.

Police officials said teachers blocked most federal and local roadways in an attempt to stop a march in support of Oaxaca state Governor Ulises Ruiz, who last week ordered police to force protesters from Oaxaca City’s main square where they had camped out to demand a salary hike.

Protesters have called for Ruiz’s ouster and mounted the blockades to try to turn back buses carrying government supporters, many of whom were believed to have been summoned by the governor himself.

Mexican newspaper Reforma reported on its website that the pro-Ruiz march, which was organised by local business groups, took place after only an hour’s delay.

Police said the protesters torched at least two buses, and some attended the blockades armed with sticks, machetes, and guns, police said.