Police regained control of Brazil’s main government complex on Sunday evening after thousands of supporters of rightwing former president Jair Bolsonaro stormed the Congress, supreme court and presidential palace.

Social media footage earlier showed crowds vandalising the interiors of the three institutions in Brasília in scenes reminiscent of the US Capitol invasion two years ago by supporters of ex-president Donald Trump.

Clad in the yellow and green of the Brazilian flag, the protesters called for a military coup d’état, demanding that the election victory of Luiz Inácio Lula da Silva be overturned and the leftwing leader imprisoned. Police said 300 people were arrested.

Although the government buildings were unoccupied and Congress not in session, the breaches are likely to raise doubts about the security of Brazil’s political and judicial institutions. The incident also presents tough choices for Lula, who took the presidency just a week ago promising to unite the nation but will be under pressure to crack down on Bolsonaro’s radical supporters.

“There is no precedent in the history of our country for what these people did. They have to be punished. And we are going to find out who are the financiers of these vandals,” said Lula, who was outside the capital on Sunday visiting a city in São Paulo state affected by recent flooding.

“They will all pay with the force of law for this irresponsible act, this anti-democratic act, this act of vandals and fascists.”

Television footage showed police firing stun grenades and using pepper spray on demonstrators, who then stormed barricades and mounted a ramp up to the roof of parliament, alongside the building’s iconic white double domes. A video clip circulated online of a mounted police officer falling off his horse after being violently set upon by a group of rioters.

Smartphone images emerged of ransacked rooms with damaged furniture, files strewn across the floor and water spraying from fire sprinklers. Many intruders covered their faces with masks.

Bolsonaro, who is currently in Florida, said on Twitter that peaceful demonstrations were part of democracy, but that the actions on Sunday crossed the line. However, he rejected Lula’s accusations that he had encouraged the deeds.

The nationalist former army captain had defied tradition by not attending Lula’s inauguration last week, instead travelling to the US.

Like his erstwhile American counterpart Trump, Bolsonaro has long cast doubt on the integrity of Brazil’s electronic voting system. His political party launched a legal challenge to annul the election result, but it was rejected by a court.

The disorder occurred after protesters descended on the capital in busloads on Sunday for a planned demonstration. Police had ejected trespassers from the sites by the evening, as calm was largely restored to the main avenue in the capital where dozens of stragglers remained.

Questions will be asked of the new defence minister, José Múcio Monteiro, given his delicate treatment of activists who refuse to accept Bolsonaro’s defeat and have for months camped outside military bases calling for a putsch by the armed forces. They claim without evidence that the ballot was rigged and accuse top judges of political bias and censorship.

“This absurd attempt to impose will by force will not prevail,” Flavio Dino, Brazil’s minister of justice and public security, said on Sunday night.

Prominent lawmakers and allies of Lula condemned the actions as an attack on democracy.

Rodrigo Pacheco, speaker of the senate, posted on social media: “I vehemently repudiate these anti-democratic acts, which must urgently face the rigour of the law.”

Gleisi Hoffman, president of Lula’s Workers’ party, said authorities in the federal district, where Brasília is located, had failed to provide adequate security.

“It is a crime announced against democracy, against the will of the polls and by other interests. [The] governor and his security secretary are responsible for what happens,” she wrote on Twitter.

The chorus of censure was joined by the chief justice of the supreme court. Rosa Weber pledged that the “terrorists who participated in these acts will be duly tried and exemplarily punished”. Another top judge said the organisers and financiers of the event, as well as public officials involved in “anti-democratic acts”, would all face justice, too.

Soon after the attacks, the governor of Brasília announced that his secretary in charge of security had been fired.

A key ally of Bolsonaro also sought to distance the far-right populist from the unrest.

Valdemar Costa Neto, the head of the ex-president’s Liberal party, said that the rioters “do not represent Bolsonaro”.

Politicians and leaders around the world denounced the acts and voiced support for the Lula administration.

US president Joe Biden — whose opponent in the 2020 election, Trump, also refused to concede — described the attack as “outrageous.”

“Brazilian democracy will prevail over violence and extremism,” said the EU’s high representative for foreign affairs, Josep Borrell.

Additional reporting by Carolina Ingizza in São Paulo