Backers of President Donald Trump, some carrying guns, ramped up demonstrations on Thursday night against what he has baselessly called a rigged election, in battleground states where votes were still being counted.
The demonstrations were largely peaceful, although Trump supporters occasionally shouted with counterprotesters. Trump says the election is being stolen but there has been no evidence of fraud.
In Arizona, one of the closely contested states in the too-close-to-call race between Trump and Democratic challenger Joe Biden, Trump and Biden supporters briefly scuffled outside the Maricopa County Elections Department in Phoenix.
Several heavily armed right-wing groups assembled on the site as election workers counted votes inside, but the protests remained mostly peaceful despite mounting tension.
Local election officials continued to tabulate ballots across the country, in some cases processing an unprecedented number of mail-in ballots that accumulated as a preferred voting option during the coronavirus pandemic.
In Philadelphia, police said they arrested one man and seized a weapon as part of an investigation into a purported plot to attack the city's Pennsylvania Convention Centre, where votes were being counted.
But otherwise the scene in Philadelphia was less confrontational - festive, even - where pro-Trump and pro-Biden demonstrators were separated by waist-high portable barriers under a strong police presence.
With the future of the presidency in the balance, restive encounters also unfolded in New York and Washington as well as swing-state cities such as Milwaukee, Wisconsin; Las Vegas, Nevada; Detroit, Michigan; and Atlanta, Georgia.
On the internet, Facebook removed a fast-growing group in which Trump supporters posted violent rhetoric, as it and other social media companies tackled baseless claims and potential violence.
Trump supporters took their cue from the president, who has repeatedly and falsely claimed that mail-in votes are especially prone to fraud.
In Phoenix, Trump supporters briefly chased a man who held up a sign depicting the president as a Nazi pig behind a stage where right-wing conspiracy theorist Alex Jones was speaking.
Police intervened and broke up the altercation after the man and his small group of counterdemonstrators were surrounded by Trump activists.
"They are trying to steal the election but America knows what happened and it's fighting back," Jones told the throng of some 300 people.-Reuters