Jose Serra, the opposition candidate for Brazilian president, was attacked Wednesday during a campaign walk in the Rio de Janeiro neighbourhood of Campo Grande, allegedly by supporters of his rival Dilma Rousseff, dpa reported.
As a result of the attack, the centre-right candidate cancelled the remainder of his campaign in Rio ahead of the runoff presidential election on October 31.
Serra's advisors said a clash broke out between supporters of his Party of Brazilian Social Democracy (PSDB) and supporters of the Workers' Party (PT) of the centre-left Rousseff and of outgoing Brazilian President Luiz Inacio Lula da Silva.
Supporters of the PT shouted abuse and threw objects at Serra's party, the candidate's camp said.
After the attack, Serra got into a car that drove about 100 metres before he got out to continue his campaign walk. He was later taken to hospital, where doctors recommended that he rest. He cancelled two more events in Rio on Wednesday and was planning to return to his native Sao Paulo later in the day.
In brief comments to reporters, Serra blamed the attack on "PT shock troops" and said the group's behaviour was "typical of fascist movements."
PT Secretary General Jose Eduardo Cardozo, however, said the PT does not promote violence and that the hostile atmosphere in the campaign was triggered by the PSDB, which "started this campaign of hatred."
"I regret the incident, it is not good. Our party in no way promotes such actions. But this campaign promotes hatred, and that does not start with us," Cardozo said.
"Unfortunately it was they who started this campaign of hatred. But we are against any act of violence, and we do not accept actions like this one," he said.
According to an opinion poll released by the Vox Populi Institute on Tuesday, Lula's designated heir Rousseff has a comfortable lead ahead of the runoff. The poll shows her with 57 per cent support, to Serra's 41 per cent.