Brazilian held over alleged bomb plot to stop inauguration
The 54-year-old suspect told investigators he had come to Brasilia on 12 November to take part in protests outside the army's headquarters.
Supporters of President Bolsonaro have been demonstrating there for weeks, demanding that the security forces intervene to prevent his elected successor, Lula, from taking up office.
These hardcore supporters of the far-right president believe that the presidential election, which Lula won by a narrow margin against Mr Bolsonaro, was fraudulent, even though there is no evidence to support their claim.
Mr Bolsonaro himself had repeatedly sown doubt about Brazil's electronic voting system in the run-up to the election, thereby fuelling his supporters' mistrust of the result.
His allegations have been dismissed as baseless by Brazil's electoral court and a challenge by his party against the election result was also rejected, but many of his supporters remain convinced the election was "stolen" from him.
Police said the suspect had told them that he and fellow protesters outside the army headquarters had decided "to try to provoke an armed forces intervention" to prevent "communism from taking hold in Brazil".
They had planned to detonate a number of bombs across the capital to force the army to declare a state of emergency, in the hope of stopping the swearing-in ceremony from taking place.
Brasilia Police Chief Robson Cândido told journalists at a news conference that the group had set off the explosive device it had planted on a fuel truck parked at the city's airport, but that it had failed to go off.
The device was spotted by the truck's driver, who alerted police.
Officers managed to track the suspect to an apartment, where he was storing "an arsenal of weapons", according to Mr Cândido.
Brazil's justice minister designate, Flávio Dino, said security measures for Lula's swearing-in on 1 January would be "re-evaluated and reinforced" following the incident. "Democracy won and will win," he wrote on Twitter, referring to the election and the handover of power.