Trump's earlier comments had given some critics and supporters hope that the White House was ready to begin working on a transition with Biden's team. Not so fast, Trump would soon assure.

Trump, without using Biden's name, said that "He won" as part of a tweet that made baseless claims about a "rigged" election.

But as the president saw how his comments were being interpreted as his first public acknowledgement of a Biden victory, Trump quickly reversed course.

"He only won in the eyes of the FAKE NEWS MEDIA," Trump subsequently tweeted. "I concede NOTHING! We have a long way to go. This was a RIGGED ELECTION!"

Later on Sunday, he tweeted four words: "I WON THE ELECTION!"

There was no widespread fraud in the 2020 election. In fact, election officials from both political parties stated publicly that the election went well, and international observers confirmed there were no serious irregularities.

Trump's campaign has tried to mount legal challenges across the country, but many of the lawsuits have been thrown out and none has included any evidence that the outcome might be reversed.

Biden defeated Trump by winning back a trio of battleground states: Michigan, Wisconsin and Pennsylvania, and topped the 270 electoral vote threshold to clinch the presidency. Biden so far has 78.8 million votes, the most ever by a winning candidate, to Trump's 73.1 million.

"If the president's prepared to begin to recognise that reality, that's positive," Biden's incoming chief of staff, Ron Klain, told NBC's Meet the Press.

Still, Klain said, "Donald Trump's Twitter feed doesn't make Joe Biden president or not president. The American people did that."

Nearly two weeks after Election Day, Trump has neither called Biden nor made a formal concession, and White House officials have insisted that they are preparing for a second term.

Former President Barack Obama, in an interview conducted and aired Sunday on CBS' 60 Minutes, said he would remind Trump that, as president, he is a public servant and a temporary occupant of the office.

"And when your time is up then it is your job to put the country first and think beyond your own ego, and your own interests, and your own disappointments," Obama said.

"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."

In recent days, Trump appeared to be inching closer to acknowledging the reality of his loss.

In comments Friday in the Rose Garden about a coronavirus vaccine, Trump said his administration would "not be going to a lockdown" to slow the spread of COVID-19, and added that "whatever happens in the future, who knows which administration it will be? I guess time will tell."

Trump on Sunday renewed his groundless attacks on an election technology firm, Dominion Voting Systems, without evidence of any serious irregularities.

Dominion has said it "denies claims about any vote switching or alleged software issues with our voting systems".

The Cybersecurity & Infrastructure Security Agency, a federal agency that oversees US election security, said in a statement last week that the "November 3rd election was the most secure in American history".

The agency said, "There is no evidence that any voting system deleted or lost votes, changed votes, or was in any way compromised."

Australian Associated Press