"We were getting ready to win this election. Frankly, we did win this election," Trump said, addressing an extraordinary press conference from the White House at 2.30 am.
"This is a major fraud on our nation. We want the law to be used in a proper manner. So we'll be going to the US Supreme Court. We want all voting to stop," said the President, who monitored election returns with members of his family in the living room of the White House residence.
The Biden campaign soon hit back, calling the President's bid to stop vote counting "outrageous" and "unprecedented," and saying its legal teams were ready to fight him in the courts.
"The counting will not stop. It will continue until every duly cast vote is counted," said the Biden campaign.
Polls have closed and voting has stopped across the country, but election laws in US states require all votes to be counted, and many states routinely take days to finish counting legal ballots. More votes stood to be counted this year than in the past as people voted early by mail and in person because of the coronavirus pandemic.
Trump has won the battlegrounds of Florida, Ohio and Texas, erasing Biden's hopes for a decisive early victory. Biden has won Arizona and Wisconsin and his hopes are pinned on the so-called "blue wall" states of Michigan and Pennsylvania that sent Trump to the White House in 2016.
Trump was ahead in all three states in partial counts, with Democratic mail-in ballots still to be tallied. Winning those three states would be enough to give Biden an Electoral College victory.
"We believe we're on track to win this election," Biden said in a speech at his hometown in Delaware earlier.
Biden leads 227 to 213 over Trump in the fight for 270 Electoral College votes.
In tweets, Trump had accused the Democrats of "stealing the election", without offering evidence. Biden had said in his speech shortly afterwards: "It's not my place or Donald Trump's place to declare the winner of this election. It's the voters' place."
(With inputs from Reuters and AFP)
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