Brazil's attorney general has requested an investigation into an alleged US government funding program that targeted the Supreme Federal Court (STF), days before the presidential election.

Attorney General Jorge Messias said on Thursday that foreign political interests seeking to interfere in Brazilian institutions or influence decisions belonging to Brazilian voters "cannot be tolerated."

The request followed a report by The Guardian newspaper that the administration of US President Donald Trump planned to direct funds toward a campaign opposing the top court.

The report said a $1 million US grant was allocated to a "Countering Lawfare and Censorship in Brazil" project to support civil society groups opposing judicial overreach and censorship by the court.

Messias described the reported initiative as "an important alert for Brazilian sovereignty" and said the issue was particularly sensitive because of the electoral process.

The attorney general's office asked the Federal Police and federal prosecutors to examine the origin, destination and purpose of the funds, and determine whether they could constitute foreign interference in Brazil's political or electoral process.

The reported $1 million grant is part of a broader package of more than $175 million from a US State Department human rights fund for projects worldwide, according to The Guardian.

The project comes amid tensions between supporters of former President Jair Bolsonaro and the Supreme Court, particularly Justice Alexandre de Moraes.

Bolsonaro was sentenced to 27 years in prison after he was convicted of attempting to overturn the result of the 2022 presidential election.

Brazil is set to hold a presidential election on Sunday, with President Luiz Inacio Lula da Silva seeking another term. Flavio Bolsonaro, the former president's son, is among the candidates.

The US has not publicly confirmed that the reported funding was intended to interfere in the election. (AA)