Brazil's Congress has opened an inquiry into the January 8 storming of key government buildings in the capital by violent demonstrators who denied the electoral victory of the recently inaugurated President Luiz Inacio Lula da Silva.

In a joint session of its two chambers on Wednesday, the parties began selecting the 16 senators and 16 representatives who will sit on the committee, with opposition parties and the government's allies battling to appoint its chair and rapporteur.

Lula's Workers Party had tried to avoid the congressional inquiry, hoping to leave investigations to law enforcement and keep lawmakers' focus on his legislative agenda.

The right-wing opposition has pushed for an inquiry as a way to blame his new government for security failures in Brasilia that day.

The government fears the inquiry will be a political side-show, firing up supporters of former president Jair Bolsonaro and distracting from Lula's proposed tax reform and budget rules meant to keep a lid on public debt and boost social programs to address inequality, government allies said.

The opposition, which has a strong position in Congress, plans to stack the committee with enough lawmakers to run the hearings and put the minority Lula government on the defensive, according to the right-wing Liberal Party (PL).

"We want to chair the committee. Our party wants to know why the government did not deploy police on the streets," said a spokesman for the PL, Bolsonaro's party and the largest in Congress.

Representatives proposed by the PL include the former president's son Eduardo Bolsonaro, his former intelligence chief Alexandre Ramagem and Andre Fernandes, who called for the inquiry even though he is being investigated by the Supreme Court for supporting the January 8 storming.

The demonstrations are being investigated by the top court, public prosecutors and the federal police in probes that may carry more serious consequences for Bolsonaro and his supporters, 800 of whom face charges for vandalism and defending a military coup.

Bolsonaro denies involvement

Bolsonaro, who has denied any responsibility for the storming as he was not in Brazil at the time, was called to testify at federal police headquarters on Wednesday morning.

He was questioned for over two hours at the federal police headquarters in Brasilia, but left in a vehicle with tinted windows without speaking to reporters.

His spokesperson Fabio Wajngarten said the former president condemned the events in his police hearing.

Thousands of Bolsonaro's supporters stormed Congress, the Supreme Court and the presidential palace in Brasilia on January 8, a week after Lula took office.

In scenes reminiscent of the January 6, 2021, riots in Washington by supporters of ex-president Donald Trump — Bolsonaro's political role model –– they trashed offices, smashed windows, vandalised artworks and called for the military to intervene to oust Lula.

Some 1,800 people have been arrested.

Bolsonaro was previously interviewed by police on April 5 in relation to an accusation that he tried to illegally import millions of dollars worth of jewellery gifted by Saudi Arabia.