Congress candidate killed in Mexico City suburb

A leftist candidate for Mexico's Congress was murdered in a suburb of the capital on Tuesday, becoming the fourth politician killed ahead of Sunday's midterm elections.

Miguel Angel Luna was running to represent the Valle de Chalco district in the central State of Mexico when he was killed, his Democratic Revolution Party said on Twitter.

The party did not provide more details but local media said he was shot in his campaign office.

He is the first federal candidate to be killed in the runup to the election. Two mayor hopefuls were assassinated in the southern state of Guerrero and another in neighboring Michoacan.

Mexican elections are often marked by spasms of violence.

Teachers from a radical union have vowed to block people from voting in the southern states of Guerrero and Oaxaca.

On Monday, offices of election authorities were attacked in both states, and protestors stole and burned thousands of ballots.