The shooting over the weekend of an official in Brazil's leftist Workers' Party (PT) by a supporter of rightwing President Jair Bolsonaro has inflamed fears of more political violence ahead of a heated election in October.

The local party official's death was the most dramatic case this year of a rising tide of political violence in the world's fourth-largest democracy, tracked by the Electoral Investigation Group (GIEL) at the Federal University of Rio de Janeiro.

"The increase in violence has a lot to do with the current political climate," said GIEL coordinator Felipe Borba. "Not because it's polarized, elections have always been polarized ... but because polarization is being fed by a discourse of hatred."