Late on Thursday, Philadelphia police said they were investigating an alleged plot to attack the city’s Pennsylvania Convention Center, where votes were being counted. Police took at least one man into custody and seized a weapon. No injuries were reported.
A large number of police officers remain on the scene.
Security has been increased around the Convention Center following the arrest.
Footage taken from above shows an empty silver Humvee being investigated by authorities.
Pennsylvania is one of a number of key battleground states that is being contested between Donald Trump and Joe Biden.
Currently Donald Trump has the lead but this is being eroded as more mail-in ballots, which traditionally favour Democrats, are counted.
With some 95 percent of ballots cast having been counted the sitting president has a lead of 22,576 votes in the state.
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Speaking from the White House on Thursday the president accused his Democrat rivals of “trying to steal an election”.
He commented: “We cannot allow anyone to silence our voters and manufacture the results.
“They are trying to steal an election, they’re trying to rig an election.
“They are trying obviously to commit fraud.
“Democrat officials never believed they could win this election honestly.”
Independent election experts insist there is no evidence of widespread electoral fraud.
President Trump also suggested legal disputes over the election could end up in the Supreme Court.
Mr Trump’s comments were condemned by Larry Hogan, the Republican Governor of Maryland.
He tweeted: “There is no defense for the President’s comments tonight undermining our Democratic process.
“America is counting the votes, and we must respect the results as we always have before.
“No election or person is more important than our Democracy.”