By Anthony Boadle
BRASILIA (Reuters) - Brazil's President Jair Bolsonaro plans to appeal to the Supreme Court over a national electoral authority ruling that rejected his campaign's complaint about radio station ads, raising tensions just three days before a runoff vote that opinion polls predict he is likely to lose to his leftist adversary.
Separately, Bolsonaro cut short a campaign trip on Wednesday and returned to Brasilia where he called a meeting with the commanders of the armed forces, Brazilian media reported. This further raised concerns about disruptions before or after Sunday's vote pitting Bolsonaro against former President Luiz Inacio Lula da Silva.
"We will take this to the last consequences, within the limits of the Constitution, to uphold the findings of our audit," the far-right populist told reporters late on Wednesday.
He said his lawyers would file an appeal against the Superior Electoral Tribunal (TSE) that threw out a complaint by the president's campaign that radio stations have been giving more spots for ads by Lula.
In its ruling on Wednesday, the TSE asked Brazil's top public prosecutor to investigate the possible intention of the Bolsonaro camp to disrupt the election in its final days.
Lula said the ads claim was a sign of despair and put it down to the incompetence of Bolsonaro's campaign handlers.
"He has a right to kick and cry like someone who knows he is losing. He is desperate," Lula said in a radio interview.
Opinion polls this week show Lula is leading by 5 or 6 percentage points and Bolsonaro has not managed to narrow the race in its final week.
Bolsonaro's allies accuse pollsters of systematic bias against the president, noting that he won nearly 10 percentage points more in the first round of voting on Oct. 2 than polls had shown during the campaign.
The president has repeatedly criticized the country's electronic voting machines for allegedly being open to fraud, without providing evidence, raising fears that he might not concede defeat if he loses.
Now he has claimed fraud involving campaign radio spots, adding to expectations that he will contest the result if he loses to Lula.
Neither the Defense Ministry nor the Army replied to a request for confirmation that the military commanders met with Bolsonaro on Wednesday night.
Bolsonaro has tried to get the military to publicly endorse his re-election bid along with his complaints about the electronic voting machines that he says cannot be audited.
The armed forces conducted an investigation into the electoral system during and after the first-round vote and according to Brazilian media reports found nothing irregular. O Globo newspaper reported two weeks ago that Bolsonaro had ordered the military not to publish that finding.
Former senior military officers consulted by Reuters say the armed forces will stick to their constitutional role in protecting Brazil's democracy and would not back Bolsonaro if he refused to leave power.
"I think it is wrong not to publish the results of that report because it gives rise to speculations and alarmist interpretations," said retired cavalry general Paulo Chagas.
(Reporting by Anthony Boadle, Maria Carolina Marcello and Ricardo Brito; Editing by Frances Kerry)