A Brazilian official from the country's socialist opposition party was slain on Saturday by a federal prison officer who stormed the official's birthday party while yelling support for right-wing President Jair Bolsonaro.

According to state civil police and a witness, Workers' Party (PT) official and municipal guard Marcelo Arruda was celebrating his birthday in the southern city of Foz de Iguacu, Parana, when the suspect Jorge Jose da Rocha Guaranho entered the private gathering and shot him to death.

Guaranho was killed when Arruda, who was reportedly also armed, opened fire in retaliation, according to a statement from the Workers' Party.

"Another dear comrade died this morning as a result of intolerance, hatred, and political violence," said Gleisi Hoffmann, the national president of the PT, in a statement.

Guaranho entered the gathering first, brandishing a firearm while insulting attendees and praising Bolsonaro. According to partygoer and witness Aluizio Palmar, a Brazilian journalist, he departed but returned around 15 to 20 minutes later, pointing a gun squarely at Arruda.

Arruda introduced himself as a member of the security forces and commanded Guaranho to disarm.

According to the PT statement, police, and security footage, both men exchanged gunfire and shot and killed each other.

The double shooting occurred months before the October presidential election in Brazil. The violence indicates the increasing political polarization between the two major parties in the country.

Luiz Inacio Lula da Silva, former president of Brazil, is the PT's candidate and currently leads Bolsonaro, seeking re-election, in the polls.

Bolsonaro has alluded to the prospect that he may not accept an electoral defeat. He has already cited baseless allegations of election fraud and problems with the electronic voting system in Brazil.

Bolsonaro stated on Twitter following Saturday's shooting that he will not accept "support from those who practice violence against opponents."