US President Joe Biden has admitted he "had a bad night," "screwed up" and "made a mistake" in a televised debate against former President Donald Trump last week. But he vowed to stay in the presidential election contest.

Biden spoke in an interview during a radio show that aired on Thursday. The 81-year-old's shaky debate performance has fueled concerns about his age, leading a congressional Democrat to seek his withdrawal from the election race.

The president said he "didn't have a good debate" during his 90 minutes on stage. But Biden asked listeners to look at what he has accomplished in three and a half years of his presidency. He stressed he had "led the economy back from the brink of collapse."

He also declared his intention to beat Trump and win the election as he had done in 2020.

Biden is scheduled to deliver a speech during an event to celebrate Independence Day on Thursday. He is also due to be interviewed for a TV program and give an address in a battleground state over the next few days.