Brazil's new President Luiz Inacio Lula da Silva gestures at supporters at Planalto Palace after his inauguration ceremony at the National Congress, in Brasilia, on Jan. 1. AFP-Yonhap

Brazil's Luiz Inacio Lula da Silva was sworn in as president on Sunday, and in his first address expressed optimism about plans to rebuild while pledging that members of outgoing Jair Bolsonaro's administration will be held to account.

Lula is assuming office for the third time after thwarting far-right incumbent Bolsonaro's reelection bid. His return to power marks the culmination of a political comeback that is thrilling supporters and enraging opponents in a fiercely polarized nation.

''Our message to Brazil is one of hope and reconstruction,'' Lula said in a speech in Congress' Lower House after signing the document that formally instates him as president. ''The great edifice of rights, sovereignty and development that this nation built has been systematically demolished in recent years. To re-erect this edifice, we are going to direct all our efforts.''

Sunday afternoon in Brasilia's main esplanade, the party was on. Tens of thousands of supporters decked out in the red of Lula's Workers' Party cheered after his swearing in.

They celebrated when the president said he would send a report about the prior administration to all lawmakers and judicial authorities, revoke Bolsonaro's ''criminal decrees'' that loosened gun control, and hold the prior administration responsible for its denialism in the face of the COVID-19 pandemic.

''We do not carry any spirit of revenge against those who sought to subjugate the nation to their personal and ideological designs, but we are going to ensure the rule of law,'' Lula said, without mentioning Bolsonaro by name. ''Those who erred will answer for their errors, with broad rights to their defense within the due legal process.''

Lula's presidency is unlikely to be like his previous two mandates, coming after the tightest presidential race in more than three decades in Brazil and resistance to his taking office by some of his opponents, political analysts say.

The leftist defeated Bolsonaro in the Oct. 30 vote by less than 2 percentage points. For months, Bolsonaro had sown doubts about the reliability of Brazil's electronic vote and his loyal supporters were loath to accept the loss.

Many have gathered outside military barracks since, questioning results and pleading with the armed forces to prevent Lula from taking office.

His most die-hard backers resorted to what some authorities and incoming members of Lula's administration labeled acts of ''terrorism'' ― which has prompted security concerns about inauguration day events.

Lula will have to navigate more challenging economic conditions than he enjoyed in his first two terms, when the global commodities boom proved a windfall for Brazil.

President Luiz Inacio Lula da Silva, left, and his wife Rosangela Silva form a heart with their hands after he was sworn in as new president at the Planalto Palace in Brasilia, Brazil, Sunday, Jan. 1. AP-Yonhap

At the time, his administration's flagship welfare program helped lift tens of millions of impoverished people into the middle class. Many Brazilians traveled abroad for the first time. He left office with a personal approval rating of 83 percent..