WASHINGTON, Nov. 27 (Xinhua) -- U.S. President-elect Donald Trump claimed on Sunday that he would have won the popular vote if millions of people didn't vote "illegally" on Nov. 8, the Election Day.

"In addition to winning the Electoral College in a landslide, I won the popular vote if you deduct the millions of people who voted illegally," Trump wrote on Twitter.

"Serious voter fraud in Virginia, New Hampshire and California -- so why isn't the media reporting on this? Serious bias -- big problem!" Trump twittered hours later, but again did not present any evidence. His Democratic rival Hillary Clinton won all the three states.

U.S. election law experts quickly rejected the president-elect's claims as farfetched, while the fact-checker PolitiFact said Trump's claim was highly suspicious.

"Trump is the first winning candidate to question the legitimacy of the process that gave him the White House," Timothy Naftali, a history professor at New York University, was quoted by local media as saying.

Trump's latest claim came after Green Party presidential candidate Jill Stein requested a vote recount.

On Saturday, Trump said Stein's move was a "scam," accusing her of using the recount "to fill her coffers with money, most of which she will never even spend on this ridiculous recount." However, he did not give any evidence for such an allegation.

Stein filed for a vote recount in the state of Wisconsin Friday, and promised to ask for the same in Michigan and Pennsylvania next week. She won approximately 1 percent of the vote in each of the three states.

Democratic presidential nominee Hillary Clinton's campaign said Saturday that it will join Stein's effort to make sure the vote recount is "fair to all sides."

Trump won all three states by a narrow margin in the presidential election, leading his major rival Democrat Hillary Clinton with just over 100,000 votes in all three states.

Clinton is now ahead in the popular vote by about 2.2 million votes, though Trump won the Electoral College by beating Clinton in key battleground states like Pennsylvania, Ohio and Florida.

The Obama administration has repeatedly denied any major voter frauds, stressing that the election results "accurately reflect the will of the American people."

U.S. electors will meet on Dec. 19 to certify the votes of the Electoral College.