Lula was inaugurated last week but was in Sao Paulo on an official state visit when the protests began.
I condemn the assault on democracy and on the peaceful transfer of power in Brazil.
Brazils democratic institutions have our full support and the will of the Brazilian people must not be undermined.
Supporters of Brazilian former President Jair Bolsonaro invade the Palácio do Planalto in BrasiliaTON MOLINA/AFP via Getty Images
I look forward to continuing to work with@LulaOficial.
US Secretary of State Antony Blinken also tweeted that using violence to attack democratic institutions is always unacceptable.
Bolsanaro, who has refused to concede the election to Lula, is currently in Florida.
Some U.S. politicians are demanding he is extradited to Brazil.
He tweeted to say public demonstrations were democratic but that invasions of public buildings went too far.
Local reports claim around 3,000 people were involved in the invasions, with around 300 arrested so far.
