Donald Trump appears to have acknowledged for the first time that Joe Biden won the US presidential election before launching a Twitter blitz of false claims that it was “rigged”.

Mr Trump is yet to officially concede the presidential election, which is stalling the normal process of preparing for a new administration.

Mr Biden’s incoming White House chief of staff, Ron Klain, has called for the transition team’s efforts to be signed off this week so Mr Biden can receive national security briefings and deal with COVID-19.

However, after using the words “he won” in a Tweet referencing Mr Biden, Mr Trump has doubled down on his unsubstantiated claims of fraud, dodgy software and Democrats “stealing” votes.

“He won because the Election was Rigged,” Mr Trump tweeted on Sunday (local time).

“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!”

He also wrote: “He only won in the eyes of the FAKE NEWS MEDIA. I concede NOTHING! We have a long way to go. This was a RIGGED ELECTION!

“All of the mechanical “glitches” that took place on Election Night were really THEM getting caught trying to steal votes. They succeeded plenty, however, without getting caught. Mail-in elections are a sick joke!”

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! https://t.co/Exb3C1mAPg

— Donald J. Trump (@realDonaldTrump) November 15, 2020

Mr Biden has won 306 votes in the state-by-state Electoral College system that determines the presidential winner, according to Edison Research. He needed 270 to secure a majority.

The Democratic former vice-president also won the national popular vote by more than 5.5 million votes, or 3.6 percentage points.

The Trump administration’s refusal to recognise Mr Biden as the winner has prevented him from gaining access to government office space and to funding normally afforded to an incoming administration to ensure a smooth transition.

Mr Biden has spent days huddled with advisers as he weighs Cabinet appointments, fields congratulatory calls from world leaders and maps out the policies he will pursue after being sworn in on January 20.

Mr Biden has also contacted drug-makrt Pfizer about its promising vaccine as Dr Anthony Fauci warned that a delayed hand-off was especially problematic during a public health crisis.

“Of course it would be better if we could start working with them,” said Dr Fauci, head of the National Institute of Allergy and Infectious Diseases, likening the process to runners passing on the baton in a relay race.

“You don’t want to stop and then give it to somebody,” he said. “You want to just essentially keep going.”

Mr Trump’s campaign has filed lawsuits seeking to overturn the results in multiple states, though without success, and the President has put his personal lawyer Rudy Giuliani in charge of the challenges.

Legal experts say the litigation stands little chance of altering the outcome of the election and many of the cases have already either been dropped or rejected.

Election officials have said there is no evidence of major irregularities and the election was the most secure ever.

Pro-Trump protests get heated

On Saturday (local time), tens of thousands of flag-waving Trump supporters rallied in Washington to echo his claims of election fraud.

The march was largely peaceful, though numerous scuffles broke out between Trump supporters and counter-protesters that continued after dark.

After night fell, the relatively peaceful demonstrations in Washington turned from tense to violent.

Videos posted on social media showed fistfights, projectiles and clubs as Trump supporters clashed with those demanding they take their MAGA hats and banners and leave.

The tensions extended to Sunday morning (local time)with charges including assault and weapons possession, were filed against those arrested, officials said. Two police officers were injured and several firearms were recovered by police.

The city’s police force arrested at least 10 people, including several who were charged with assault.

Members of Antifa and Proud Boys clash in Washington. Photo: Getty

Mr Trump himself had given an approving nod to the gathering Saturday morning by dispatching his motorcade through streets lined with supporters before rolling on to his Virginia golf club.

People chanted “USA, USA” and “Four more years,” and many carried American flags and signs to show their displeasure with the vote tally.

Dozens of Proud Boys, a far-right group, marched in the streets, some wearing helmets and ballistic vests, while members of the loose far-left movement known as Antifa staged their own counter-demonstrations.

-with AAP