Former US President Donald Trump has blasted the federal indictment against him as "ridiculous and baseless" in his first public appearance since the charges were announced.

The indictment unsealed on Friday charges the former president on 37 counts, including willful retention of national defense information.

In a speech at a Republican convention in the southern state of Georgia on Saturday, Trump asserted his innocence and accused President Joe Biden of trying to undermine his presidential campaign for 2024.

"The ridiculous and baseless indictment of me by the Biden administration's weaponized Department of Injustice will go down as among the most horrific abuses of power in the history of our country," Trump said.

He added that "the only good thing about it is it's driven my poll numbers way up."

Trump is the current front-runner for the Republican nomination in the presidential election next year.