WASHINGTON, July 24, 2024 (AFP) - US President Joe Biden will give what could be his final Oval Office speech Wednesday to explain why he dropped out of November's election and deny that he will spend six months as a lame duck.

With the world's eyes already on a looming clash between Vice President Kamala Harris and Donald Trump, Biden will insist in his address to the nation that he still has work to do despite his historic decision to bow out.

The 81-year-old Democrat said on X he would discuss "what lies ahead, and how I will finish the job for the American people" in the primetime televised event at 8:00 pm (0000 GMT Thursday).

The speech, expected to last eight to ten minutes, will be Biden's first since stepping aside from the race on Sunday after weeks of pressure following a disastrous debate performance against Trump.

He had promised in his withdrawal announcement -- made while he was isolating with Covid at his Delaware beach home -- that he would give Americans more details on his stunning decision.

It comes just over a week since his last Oval Office address following an assassination attempt against Trump on July 13, but is only the fourth of his presidency overall -- and could well be his last.

With Harris, who has effectively clinched the Democratic presidential nomination, and Trump both back on the campaign trail, Biden will be fighting an uphill battle to show Americans he is not yesterday's man.

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.

The veteran Democrat insists he still has much to offer, with a particular focus on the economy and on achieving an elusive ceasefire in Israel's war against Hamas in Gaza.

- 'Not going anywhere' -

"I'm not going anywhere," a hoarse Biden said as he called Harris at a campaign meeting in Delaware on Monday, adding that he was going to be "working like hell" both as president and to campaign.

Biden, who meets Israeli Prime Minister Benjamin Netanyahu at the White House on Thursday, added that "we're on the verge" of agreeing a ceasefire.

He would not be the first US president to chase a legacy-defining Middle East peace deal, after Jimmy Carter, Bill Clinton and even Donald Trump before him.

But in a sign of the way things are already moving on, Netanyahu will sit down separately with Harris, while Trump said in a post on his Truth Social media platform that he will meet with the Israeli leader Friday at the Republican's Mar-a-Lago resort in Florida.

With the clock ticking on his presidency, Biden said on X late Tuesday that it was "great to be back at the White House" after returning from Delaware and that he had met his national security team for a briefing.

Biden's decision to drop out has however injected a huge dose of enthusiasm into a Democratic Party that had been plunged into chaos by the debate over his age.

An exuberant Harris was cheered to the rafters on Tuesday as she held a campaign rally in the battleground state of Wisconsin, her first since saying she had secured the delegates necessary for the nomination.

She could be nominated as soon as early August in a virtual vote by Democratic delegates ahead of the party's convention in Chicago just over two weeks later.

For Harris the challenge will now be to maintain the initial burst of enthusiasm in her party -- and then to translate it into success at the ballot box in November.

Harris led Trump slightly in a poll conducted this week after Biden dropped out, but she remains vulnerable in particular to attacks on her lackluster first two years in the White House.