Washington DC - US President Joe Biden dismissed doubts that he is not fit for another term because of his age in his first interview since announcing his re-election bid last month.

"I have acquired a hell of a lot of wisdom and know more than the vast majority of people," the 80-year-old Democrat said in an interview with broadcaster MSNBC that aired on Friday night.

"And I'm more experienced than anybody that's ever run for the office. And I think I've proven myself to be honorable as well as also effective."

Biden entered the White House in 2021 as the oldest person ever sworn into the presidency. If he wins re-election in 2024, he will be 86 by the end of his second term.

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Biden's age and suitability for one of the world's most demanding jobs have long been a source of debate, including in his own party. Polls have also consistently showed there is little enthusiasm among Americans for an electoral rematch between him and Republican frontrunner Donald Trump.

In his conversation with 11th Hour host Stephanie Ruhle, Biden also defended his decision to send 1,500 US troops to the southern border, insisting that they were "not there to enforce the law," but only to free up border agents.

The president also defended his son Hunter, a lightning rod for right-wing attacks and now a reported target of the Justice Department: "My son has done nothing wrong. I trust him. I have faith in him."