US President-elect Donald Trump has said, in a tweet, that he won the popular vote in the 8 November election "if you deduct the millions of people who voted illegally".
However, he provided no evidence of voter fraud.
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— Donald J. Trump (@realDonaldTrump) November 27, 2016
The allegation by Mr Trump comes as Democratic rival Hillary Clinton's lead in the popular vote has surpassed two million votes and is expected to grow to more than 2.5 million as ballots in populous states such as California continue to be tallied.
Mr Trump won the required votes in the Electoral College to secure the presidency.
Mrs Clinton's legal team said on Saturday it had agreed to participate in a recount of Wisconsin votes after the state's election board approved the effort requested by Green Party candidate Jill Stein, which Mr Trump has called "ridiculous".
The US presidential race is decided by the Electoral College, based on a tally of wins from the state-by-state contests, rather than by the national vote.
Mr Trump has surpassed the 270 electoral votes needed to win the White House.
The Electoral College results are expected to be finalised on 19 December and Mr Trump will take office on 20 January.
"It would have been much easier for me to win the so-called popular vote than in the Electoral College in that I would only campaign in three or four states instead of the 15 states that I visited," Mr Trump added in follow-up tweets.
Several hours later, he tweeted again without citing evidence: "Serious voter fraud in Virginia, New Hampshire and California - so why isn't the media reporting on this? Serious bias - big problem!"
Serious voter fraud in Virginia, New Hampshire and California - so why isn't the media reporting on this? Serious bias - big problem!— Donald J. Trump (@realDonaldTrump) November 28, 2016
Mrs Clinton won all three states.
A spokesman for Mr Trump did not immediately respond to a request for comment.