Brazilian security forces cleared protest camps and arrested 1,500 people as President Luiz Inacio Lula da Silva condemned "acts of terrorism" after a far-right mob stormed the seat of power, unleashing chaos on the capital.

Hundreds of soldiers and police mobilized to dismantle an improvised camp outside the army's headquarters in Brasilia.

Some 3,000 supporters of ex-president Jair Bolsonaro had set up tents and ran riot inside the presidential palace, Congress and Supreme Court for around four hours Sunday.

Lula, who took office on January 1 after a divisive election win over Bolsonaro, returned to work in the pillaged presidential palace strewn with broken glass, shattered windows and doors and trashed offices.

The 77-year-old leftist who previously led Brazil from 2003 to 2010, met with the leaders of both houses of Congress and the chief justice of the Supreme Court, and joined them in condemning what many called the South American country's version of the US Capitol riots in Washington two years ago.

"The three powers of the republic, the defenders of democracy and the constitution, reject the terrorist acts and criminal, coup-mongering vandalism that occurred," they said.

Lula accepted an invitation to meet with President Joe Biden next month in Washington, US officials said.

Bolsonaro, who narrowly lost the October elections, meanwhile said on Twitter that he is in hospital in Florida with abdominal pains.

He alleged that he is the victim of a conspiracy against him and snubbed Lula's inauguration by flying to Orlando.

Bolsonaro, 67, condemned the "pillaging," but rejected Lula's claim he incited the attacks, and defended the right to "peaceful protests."

Hundreds of people gathered to defend Brazilian democracy and demand punishment for those who stormed the halls of power. They held banners that read "Respect for the people's vote."

AGENCE FRANCE-PRESSE

Lula da Silva inspects the damage at the presidential palace in Brasilia. AP

Rioters rounded up