Violence ahead of Mexico mid-term elections Published duration 6 June 2015

media caption Many protesters see voting in Mexico's election as pointless, says the BBC's Katy Watson

There has been further violence around Mexico as the country prepares for this weekend's mid-term elections.

A radical teachers' union attacked the offices of five political parties in Chiapas state in the south of the country.

Meanwhile in Guerrero state, explosive devices were thrown into a conservative party's office.

A number of candidates and numerous campaign workers have also been killed in drug-related violence.

On Sunday, Mexican voters will choose Congressmen, governors and mayors.

image copyright AFP image caption Teachers in Guerrero state have vowed to block voting on Sunday demanding better pay and a suspension of new education reforms.

image copyright AFP image caption Graffiti outside offices of the ruling Institutional Revolutionary Party (PRI) in Chiapas state reads "Assassins - there are 43 missing" , referring to the students who disappeared in Guerrero state last year.

Correspondents say it has been some of the worst political violence in Mexico's history.

The biggest concerns for electoral officers have been Guerrero and Oaxaca, where tens of thousands of ballots were burnt by protesters.

They took furniture and papers from the ruling PRI party offices in the city of Oaxaca and burnt them outside.

Others set fire to political pamphlets in front of PRI headquarters in Guerrero.

image copyright AFP image caption Teacher training students from Guerrero protested near the Secretary of the Interior building in Mexico city

Despite the unrest, electoral officials say the elections will go ahead on Sunday.

It is the first major test for President Enrique Pena Nieto who has been trying to fulfil his 2012 election promise to bring peace to Mexico after years of drug cartel violence.

Opinion polls show his Institutional Revolutionary Party (PRI) and its allies are expected to retain their majority in Congress despite concerns over their track record on security.