Joe Biden was edging closer to victory in the presidential race as he overtook the lead in the key battleground states of Pennsylvania and Georgia in potentially decisive moments.
With forecasts putting him just one state from victory, the Democratic challenger surpassed Donald Trump in the swing states on Fridays as officials continued counting votes.
Former vice president Mr Biden overhauled the Republican incumbent’s leads by more than 9,000 votes in Pennsylvania and more than 1,500 in Georgia.
Mr Trump, who is mounting legal challenges to improve his chances of re-election amid baseless allegations of fraud, has to win both of those states if he is to stay in contention.
Georgia, which the president won by more than 200,000 votes in 2016, has not been won by the Democrats since 1992. Pennsylvania, Mr Biden’s birth state, was narrowly seized from the Democrats by Mr Trump in the last election.
The president said in a statement in Friday evening: “From the beginning we have said that all legal ballots must be counted and all illegal ballots should not be counted, yet we have met resistance to this basic principle by Democrats at every turn.
“We will pursue this process through every aspect of the law to guarantee that the American people have confidence in our government. I will never give up fighting for you and our nation.”
Mr Biden was expected to address the nation later on Friday night.
He earlier appealed for calm and patience in stark contrast to Mr Trump who used an extraordinary White House press conference to scatter unsubstantiated claims that he was being cheated out of re-election as he launched legal battles.
In Georgia, the former vice president took a slender lead over Mr Trump with an estimated 98% of the ballots counted.
Both there and in Pennsylvania, recounts are expected under state law if there is less than half a percentage point between the two candidates.
The winner needs to collect 270 electoral college votes by winning states. Victory in Pennsylvania, where around 5% of ballots still need counting, would hand the presidency to Mr Biden by all counts with its 20 votes.
Georgia, with 16 electoral votes, is a more complicated scenario.
Not everyone agrees that Mr Biden has beyond all probability won in Arizona, and without that Georgia would leave him one vote short of overall victory.
He has secured victories in the battleground states of Wisconsin and Michigan, but Nevada and North Carolina also remain too close to call after Tuesday’s election.
Prime Minister Boris Johnson continued to say he has “every confidence” in the checks and balances of the American constitution and said he would “work closely with whoever is the president” but declined to comment further.
Mr Trump on Thursday night alleged he is the victim of interference from “phoney polls” as well as “big media, big money and big tech” and the Republicans took court action in attempts to improve his chances of victory.
“If you count the legal votes, I easily won. If you count the illegal votes, they can try to steal the election from us,” Mr Trump said, with multiple major US television networks pulling away from his baseless claims, which he has provided no evidence to support.
Earlier Mr Biden had used a measured tone to say “democracy is sometimes messy, it sometimes requires a little patience”. He added that he had “no doubt” he will eventually be declared the winner.
“Each ballot must be counted and that’s what we’re going to see going through now and that’s how it should be,” he said from a stage in his hometown of Wilmington, Delaware, next to his running mate Kamala Harris.
Elections are run by individual state, county and local governments, and Mr Trump’s public comments have no impact on the tallying of votes across the country.
The Trump campaign requested a recount in Wisconsin and filed lawsuits in Pennsylvania, Michigan and Georgia.
But judges in Michigan and Georgia dismissed the actions launched by the Trump campaign. Additional legal action was also expected in Nevada, the campaign indicated.
Georgia’s secretary of state Brad Raffensperger said there would be a recount in the state “with a margin that small”.
“The interest in our election obviously goes far behind Georgia’s borders. The final tally in Georgia at this point has huge implications for the entire country,” the Republican told reporters.
“The stakes are high and emotions are high on all sides. We will not let those debates distract us from our work, we will get it right and we will defend the integrity of our elections.”
The Associated Press news agency, which PA relies on to call states, has projected Mr Biden as winning Arizona and its 11 electoral college votes.
That looks likely as he has a strong lead with more than 90% of the votes tallied, but Mr Trump’s campaign disagrees and other news organisations are not so certain.
The appearance of Mr Biden coming back from behind is an artificial one. Many of the outstanding ballots are postal votes and absentee ballots which are being added to the tally later than their in-person counterparts.