WASHINGTON, July 25, 2024 (BSS/AFP) - US President Joe Biden told Americans Wednesday he quit the 2024 election to unite the country, saying in a historic Oval Office speech that it was time to pass the torch to "younger voices."

"I revere this office. But I love my country more," the 81-year-old said in an elegiac prime-time address to the nation urging his divided country to embrace democracy and shun hatred.

"The defense of democracy, which is at stake, is more important than any title," Biden said. "I have decided the best way forward is to pass the torch to a new generation. That is the best way to unite our nation."

In his first televised address since his stunning decision, Biden also hailed his Vice President Kamala Harris, 59, who is set to be the new Democratic presidential nominee.

"She's experienced. She's tough. She's capable," Biden said in just the fourth address of his presidency from behind the Resolute Desk -- and likely his last.

Biden bowed out of the race later than any other president in US history, giving in to weeks of pressure from Democrats after a disastrous debate performance against Donald Trump raised concerns about his age.

Speaking in a hushed voice after a Covid infection, Biden used the powerfully symbolic setting to insist on his achievements -- while admitting it was time to move on.

He said there was a "time and a place for new voices, fresh voices -- yes, younger voices. And that time and place is now."

- 'Never wavered' -

In a poignant sign of support for Biden after the toughest decision of his political life, most of his family sat watching him in the Oval Office as he spoke.

They included his wife Jill and daughter Ashley -- who held hands near the end of his remarks -- Biden's troubled son Hunter and a number of Biden's grandchildren.

Jill Biden later posted a letter on X thanking "those who never wavered" -- an apparent backhanded dig at the Democrats who called on Biden to quit -- and said it was "time to put that trust in Kamala."

Biden's withdrawal has upended Trump's campaign, which had previously focused on the president's age and mental acuity. Now it is Trump, 78, who is the oldest candidate in US history.

Trump, who had initially called for unity after surviving an assassination attempt on July 13, was in no mood for magnanimity after Biden's speech.

"Crooked Joe Biden's Oval Office speech was barely understandable, and sooo bad!" Trump said on social media.

Republicans have called for Biden to step down altogether, saying that if he is not fit to stand for reelection then he is not fit to serve as president.

Biden however insisted that he was no lame duck and that he would continue to work on the economy and key foreign policy issues for the rest of his time in office.

"Over the next six months I will be focused on doing my job as president," he said.

- 'Lunatic' -

One key goal is a peace deal in the Middle East -- a legacy-defining dream that many US presidents before Biden have chased.

Biden, who has been increasingly critical over Israel's military campaign in Gaza, meets Israeli Prime Minister Benjamin Netanyahu at the White House on Thursday.

But in a sign of how quickly things are changing, Netanyahu will sit down separately that day with Harris as well, as well as meeting Trump in Florida on Friday.

The US election campaign meanwhile is moving ahead at full speed without Biden.

In his first rally since Harris secured enough delegates to become the de facto Democratic nominee, Trump hit out at Harris as his "new victim."

"She is a radical left lunatic who will destroy our country," he said, accusing Harris of hiding Biden's "mental unfitness."

Earlier, the White House denied there was any "cover up" over Biden's condition.

Harris was also on the campaign trail Wednesday, telling a Black college sorority in Indianapolis that "I am fighting for our nation's future."