US President Joe Biden says he dropped out of his re-election bid because he feared that the intra-party battle over his candidacy would be a "real distraction" for Democrats and that his highest priority was to defeat Donald Trump in November.

In his first interview since quitting the race, Mr Biden, 81, said he had “no serious problem” with his health. He blamed his poor debate performance on being sick at the time, and brushed off concerns about his age and mental acuity.

The US president pledged to campaign for Kamala Harris saying he was going to do whatever his vice-president "thinks I can do to help most".

“We must, we must, we must defeat Trump,” he told US broadcaster CBS News.

Mr Biden said if he had continued his campaign, the presidential contest would have gone “down to the wire”.

"A number of my Democratic colleagues in the House and Senate thought that I was going to hurt them in the races," he said.

"And I was concerned if I stayed in the race, that would be the topic. You’d be interviewing me about, Why did Nancy Pelosi say, why did so — and I thought it’d be a real distraction.”

Former House speaker Nancy Pelosi was widely reported to have led the push to oust Mr Biden - a claim she has not exactly denied - after his halting debate performance against Trump on 27 June.

During the pre-recorded interview broadcast Sunday, Mr Biden misspoke several times but generally seemed more coherent than during the live televised debate. He chalked up his poor debate performance to illness – previously he’s also mentioned jet lag and lack of rest as factors.

As pressure continued to ratchet up, he announced his exit from the race on 21 July.

A potential battle to replace him at the top of the Democratic ticket never materialised and party support swiftly coalesced around Vice-President Harris, who has so far outperformed Mr Biden in opinion polls.

The president has said he intended to be a bridge to the next generation when he ran for the White House in 2020.

"When I ran the first time, I thought of myself as being a transition president. I can't even say how old I am. It's hard for me to get it out of my mouth.”

In the CBS interview, Mr Biden returned to the moment he decided to run against Trump – when a gathering of far-right activists in Charlottesville, Virginia in 2017 turned deadly. He accused Trump of emboldening racists and the far-right.

“Every other time the Ku Klux Klan has been involved they wore hoods so they're not identified,” he said. “Under his presidency, they came out of those woods with no hoods, knowing they had an ally.”

He also repeated his concerns about what might happen after November’s election, saying he was “not confident at all” that there will be a peaceful transfer of power if Ms Harris defeats Trump.

He went on to say that he was concerned that there would be violence if Trump loses the election.

"He means what he says,” Mr Biden said. “We don't take him seriously. He means it. All the stuff about, 'If we lose, it'll be a bloodbath’.”

"He's a genuine danger to American security,” Mr Biden said.

Trump commented at a rally in March that it would “be a bloodbath for the country” if he loses, however his campaign has repeatedly said he was referring to the economy and the auto industry and that Democrats have taken the quote out of context.

At the same time, the former president has repeatedly insisted, without evidence, that he was cheated out of victory in 2020 and has warned that there will be attempts to “rig” the vote this year. He has pledged to pardon some or all of the people convicted for rioting at the US Capitol in January 2021.

Mr Biden said he would be campaigning on behalf of Ms Harris and that he had spoken to Pennsylvania Governor Josh Shapiro about touring the state. Mr Biden was born in the working-class city of Scranton, about 120 miles (190km) north-west of New York City.

“I'm going to be campaigning in other states as well. And I'm going to do whatever Kamala thinks I can do to help most,” he said.