Donald Trump has said for the first time that president-elect Joe Biden "won" the US election - but then clarified he is not conceding.
He made the original admission in a tweet along with more unfounded claims the vote was unfairly and deliberately stacked against him.
Mr Trump wrote of his soon-to-be successor: "He won because the election was rigged.
"NO VOTE WATCHERS OR OBSERVERS allowed, vote tabulated by a radical left privately owned company, Dominion, with a bad reputation & bum equipment that couldn't even qualify for Texas (which I won by a lot!), the Fake & Silent Media, & more!"
It was a significant acknowledgement from Mr Trump, who - despite losing the Electoral College by 74 and popular vote by five million votes - has refused to accept the result.
But he later clarified in another tweet: "I concede NOTHING! We have a long way to go."
Last week Mr Trump became the first president since 1992 to fail to get re-elected, following projections Mr Biden had successfully flipped the key states of Pennsylvania, Arizona and Georgia to win the White House.
Since then, the Republican incumbent has launched legal challenges and tried to undermine the validity of the result - but failed to produce any significant evidence of the mass ballot stuffing and voter fraud he is alleging.
His supporters also gathered for protests in Washington DC over the weekend and were met by counter-protests, resulting in 20 people being arrested and at least one reported stabbing.
World leaders and former presidents - including George W Bush - have all treated the contest as finished, and sent their messages of congratulations to Mr Biden.
Prime Minister Boris Johnson is among those to already be treating the former vice president under Barack Obama as the winner and a change of administration next year as inevitable.
Only yesterday, Mr Trump suggested he could somehow remain president, saying "time will tell" who will be in the White House come January.
And on Monday, he again insisted in a tweet: "I won the election".
But the 2020 election was judged to be the "most secure in American history", according to the Cybersecurity and Infrastructure Security Agency, which spearheaded federal election protection efforts.
Former president Barack Obama, in an interview conducted and aired on Sunday on CBS' 60 Minutes, said it was not too late for Mr Trump to put the country first, adding that he would remind him that, as president, he is a public servant and a temporary occupant of the office.
"My advice to President Trump is, if you want at this late stage in the game to be remembered as somebody who put country first, it's time for you to do the same thing.
Asked if it was time for Mr Trump to concede, Mr Obama replied: "Absolutely. Well, I mean, I think it was time for him to concede probably - the day after the election."
He added: "The president doesn't like to lose and - never admits loss. I'm more troubled by the fact that other Republican officials who clearly know better are going along with this, are humouring him in this fashion. It is one more step in delegitimising not just the incoming Biden administration, but democracy generally."
In the run up to his and vice president-elect Kamala Harris' inauguration on 20 January, Mr Biden has set up a transition team to prepare for formally taking office.
Watch: What does a Joe Biden presidency in the US mean for the global economy?
The US has had the highest number of coronavirus cases and deaths of any country in the world - 10,906,000 and 245,000 respectively, according to Johns Hopkins University.
Mr Trump has been criticised by some for his actions during the pandemic - which resulted in him catching the disease in September.
Dr Anthony Fauci, one of the president's top advisers, warned recently the US "could not possibly be positioned more poorly" as it heads into winter.