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Experts and elected officials on both sides of the political aisle dismissed Donald Trump's claim that "millions" of Americans voted illegally on election day, as efforts expanded to organise recounts in swing states.
The Republican billionaire's victory on November 8 saw him clinch the crucial electoral college count, which determines the presidency, but lost the popular vote to rival Hillary Clinton by more than two million ballots.
Cloistered in his Florida resort for the long Thanksgiving weekend, the 70-year-old tycoon, who has never previously held elected office, took to Twitter to indulge in one of his customary tweet storms.
On Sunday, before returning by private jet to New York to resume interviews with potential cabinet appointees, he claimed he would have won the popular vote if it were not for "the millions of people who voted illegally."
"Serious voter fraud in Virginia, New Hampshire and California- so why isn't the media reporting on this? Serious bias- big problem!" he followed up later.
Trump, who spent the campaign warning that the result might be "rigged," is now pushing back hard as the Green Party works to secure recounts in three states which Trump won: Michigan, Pennsylvania and Wisconsin.
The campaign of Green Party candidate Jill Stein, who won a tiny fraction of the vote in each state and where Trump beat Clinton by thousands of votes, said voters had filed recount requests in more than 100 (out of 9,163) precincts in Pennsylvania, while promising that more would follow.
The party requested a statewide recount in Wisconsin on Friday and plans to request a recount in Michigan on Wednesday, the campaign said.
But observers deny any evidence of widespread fraud.
And few expect any change in the outcome of the vote, which former secretary of state Clinton conceded to Trump in an early-hours phone call on November 9.
Meanwhile, Trump increased his electoral college vote count to 306, compared to 232 for Clinton, after Michigan certified its election results and his victory there.
Republican, Democratic and independent lawmakers dismissed Trump's claims as totally unsubstantiated.
Some experts warned they set a dangerous precedent by potentially undermining trust in democracy or confidence in his leadership.
"I have not seen anything in the millions, I don't know what he was talking about," Republican Senator James Lankford told CNN.
White House spokesman Josh Earnest said "there has been no evidence produced to substantiate a claim like that."