BRASILIA, Sept 3 (Reuters) -The attempted assassination of Argentine Vice President Cristina Fernandez de Kirchner by a Brazilian has forced the main candidates in Brazil's Oct 2 presidential election to re-evaluate their security arrangements, sources said on Friday (Sep 2).

Kirchner escaped unharmed on Thursday after a 35-year-old man of Brazilian origin fired a loaded gun, just inches from her head, that failed to go off. The shooter's nationality underlined growing concerns about political violence in highly polarised Brazil in the lead-up to its election.

"This violence and political hatred that has been incited by some people is a threat to democracy in our region," said Brazil's leftist front-runner Luiz Inacio Lula da Silva in a tweet on Friday morning, in what amounted to a veiled dig at his rival, President Jair Bolsonaro.

A far-right former army captain, Bolsonaro has urged his followers to arm themselves ahead of the election or risk being "enslaved".

Critics say that his attacks against Lula, whom he labels a corrupt communist, have contributed to the fraught atmosphere.

Bolsonaro, who often campaigns in a bulletproof vest, nearly died in 2018 when he was knifed on the campaign trail.

The assassination attempt against Kirchner has prompted Bolsonaro's campaign staff to consider increasing security measures while he is on the road, a source told Reuters.

"I am sorry, it's a risk that everyone takes, I almost died in 2018 and I didn't see the left worrying about me, but it's okay," Bolsonaro told reporters on Friday afternoon while in the southern city of Porto Alegre.

"I hope that the investigation is carried out to see if it was his idea or if someone hired him to do this."

Lula's campaign was also concerned by the situation in neighbouring Argentina. Paulo Teixeira, one of his campaign managers, said that it was discussed by the team, and a new analysis of Lula's security situation will be carried out.

"We will have to take a close look at this increase in political violence in the country, which is encouraged by the current president," Teixeira told Reuters.

"My feeling is that a Brazilian trying to kill the vice president of Argentina is the result of this violence preached by the current president."

In July, an official from Lula's Workers' Party was killed by a Bolsonaro supporter, and the former president is also campaigning in a bulletproof vest.

Gustavo Petro, Colombia's leftist president, said that the attack against Kirchner was symptomatic of the increasingly tense relations between ideological rivals in the region.

"It has become common practice in Latin America to think that politics is the physical or judicial elimination of one's rival," he said. "That's pure fascism. Politics should mean freedom."