Thousands of supporters of US President Donald Trump turned out in Washington DC to back his unsubstantiated claims of voter fraud in the election.
Flag-carrying demonstrators were joined by members of far-right groups including the Proud Boys, some wearing helmets and bullet-proof vests.
The largely peaceful demonstration saw some violence later in the evening, as Trump supporters and counter-protesters clashed in several skirmishes.
Joe Biden won the 3 November election.
On Friday, he solidified his victory with a projected win in the state of Georgia - making him the first Democratic candidate to take the state since 1992.
He now has 306 votes in the electoral college - the system the US uses to choose its president - which far exceeds the 270 threshold to win.
However, Mr Trump has so far refused to concede. He has launched a flurry of legal challenges in key states and made unsubstantiated allegations of widespread electoral fraud - but his efforts have so far been unsuccessful.
What happened at the pro-Trump rally?
Mr Trump's supporters kicked off the demonstrations at about noon local time (17:00 GMT) on Saturday near Freedom Plaza, just east of the White House, and later headed towards the Supreme Court.
As well as more mainstream Trump supporters, members of the far-right Proud Boys and the Oath Keepers militia group were among the marchers. Conspiracy theorist Alex Jones addressed the crowd.
Mr Trump's motorcade passed the gathering demonstrators on Saturday morning and did a circuit of nearby Freedom Plaza, but he carried on to his golf club in Sterling, Virginia without addressing the crowds.
While the daytime event was largely orderly, Trump supporters clashed with counter-demonstrators in the night. Video footage posted on social media showed fights breaking out.
Officials said 20 people had been arrested on a variety of charges, including assault and weapons possession. One stabbing was reported. Two police officers were also injured.
A growing sense of a fight losing its energy
At the scene - Will Grant, BBC News, Washington DC
A gradual stream of pro-Trump supporters made its way towards Freedom Plaza, adorned with T-shirts and carrying placards which read "Stop the Steal" and "Trump 2020".
The demonstrators were also identifiable by their lack of face-masks as many participants rejected measures to contain the spread of coronavirus.
In that regard alone, this pro-Trump rally was seen by its critics as reckless and irresponsible. It took place with the United States grappling with some of its worst Covid-19 infection rates since the pandemic began, with more than 180,000 new cases and 1,400 deaths recorded in the country over the past 24 hours.
None of that appeared to matter much to the participants who excitedly greeted President Trump's motorcade as it made an impromptu pass around the plaza. They are desperate to see this election result overturned and fully back his unsubstantiated claims of election fraud and his refusal to concede.
Still, although they may deny it, there is a growing sense of a fight losing its energy and that - like it or not - these supporters will see President-elect Joe Biden in the White House in January.
What is Trump saying about the election result?
The president continues to dispute the election result. In a slew of tweets on Saturday, he said checks on ballots in Georgia were a "waste of time", alleging problems with signatures but without giving evidence.
A manual recount is to be carried out in Georgia because of the narrow margin between the two candidates, but this is not expected to change the results there.
On Friday, election officials said the vote was the "most secure in American history", the most direct rebuttal from federal and state authorities of the president's claims.
On Friday, White House spokeswoman Kayleigh McEnany told Fox News: "President Trump believes he will be President Trump, have a second term."
However, Mr Trump's efforts to overturn the result suffered three setbacks on Friday:
In Arizona, his team dropped a lawsuit seeking a review of ballots cast on Election Day after it became clear his rival's lead was unassailable. The challenge was based on a claim that some legal votes had been rejected
In Michigan, a judge rejected a request by two Republican poll watchers - who had alleged fraud in Wayne County - to block the certification of election results in Detroit
In Philadelphia, Pennsylvania, the Trump campaign's requests to invalidate several batches of mail-in ballots were rejected
What's happening with the transition?
Pressure is growing on Mr Trump to acknowledge Mr Biden's victory and help prepare the transition from one administration to another.
The General Services Administration (GSA), the government agency tasked with beginning the process, has yet to recognise Mr Biden and his running mate Kamala Harris as winners.
The Biden team have not been given access to classified security briefings, federal agencies and funding needed to ensure a smooth transition of power. Biden spokesperson Jen Psaki said this lack of access could affect Mr Biden's ability to govern.
"You need real-time information to deal with crises of the moment," she said, highlighting the impact of the pandemic. "It's imperative that our team and our experts have that access."
Adding his voice to those calls, President Trump's former chief of staff, John Kelly, said the delay in starting the transition was hurting national security. "It's not a process where you go from zero to 1,000 miles per hour," he told Politico.
A small but growing number of Republicans are also backing calls for the president-elect to be given daily intelligence briefings.