Washington/Wilmington: President Donald Trump on Sunday briefly acknowledged losing the U.S. election in a morning Twitter post but then backtracked, saying he concedes "nothing" and vowing to keep up a court fight that election-law experts say is unlikely to succeed.

President-elect Joe Biden focused on the coronavirus pandemic, setting meetings with vaccine developers as the crisis intensifies. The number of US coronavirus cases passed 11 million on Sunday, a million more new cases than a week ago and the fastest increase since the pandemic began.

Biden defeated Trump in the Nov. 3 election by the same 306-232 margin in the state-by-state Electoral College that Trump proclaimed a "landslide" when he won it in 2016. The Democratic former vice president also won the national popular vote by at least 5.5 million votes, or 3.6 percentage points, with some ballots still being counted.

Trump, pursuing long-shot litigation to contest election results in several states, made conflicting comments on Twitter. He initially appeared to admit for the first time publicly that Biden won, then reversed course. Trump also repeated unfounded claims of widespread voter fraud.

"He won because the Election was Rigged," Trump wrote, not referring to Biden by name, adding a list of complaints about vote counting. About 90 minutes later, Trump wrote: "He only won in the eyes of the FAKE NEWS MEDIA. I concede NOTHING!"

After golfing at a club he owns in Virginia, Trump said on Twitter he would soon file "big cases showing the unconstitutionality of the 2020 Election." Trump's campaign has filed lawsuits seeking to overturn the results in multiple states, without success.

Legal experts have said the Trump litigation stands little chance of altering the election's outcome, and election officials of both parties have said there is no evidence of major irregularities.

"Donald Trump's Twitter feed doesn't make Joe Biden president or not president. The American people did that," Ron Klain, Biden's choice as White House chief of staff, said on NBC's "Meet the Press."

More than a week after Biden was declared the victor by major news organizations based on state-by-state vote counts, the General Services Administration still has not recognized him as president-elect, preventing his team from gaining access to government office space and funding normally afforded to an incoming administration to ensure a smooth transition.

Without explicitly mentioning the transition, Trump praised the GSA administrator he appointed, Emily Murphy, writing on Twitter: "Great job Emily!"

Klain said Murphy's agency must formally recognize Biden, saying it is critical to ensure the president-elect receives intelligence briefings before taking office and to facilitate coordination with the White House coronavirus task force. Klain urged Congress to pass bipartisan coronavirus relief legislation by year's end. Talks on such legislation have stalled.

Some congressional Republicans and former members of Trump's administration have also called on the White House to allow Biden's transition team access to more information to prepare to govern.