Twitter has hidden a tweet by Donald Trump moments after it was posted, adding a warning that it contained disputed content that could be misleading.
The U.S. president had written early on Wednesday morning that Democrats were attempting to "steal the election", a claim for which he offered no evidence.
Trump also falsely suggested that votes could not be cast after the polls had closed.
The tweet appeared moments after his Democratic challenger Joe Biden made a televised speech saying he believed he was on course to win the 2020 presidential election.
The race was too close to call in several key battleground states at the time.
Minutes after it was posted, Twitter added the warning to Trump's tweet: "Some or all of the content shared in this Tweet is disputed and might be misleading about an election or other civic process."
The tweet was still visible after clicking through the warning, which was placed in line with Twitter's "Civic Integrity Policy".
Trump posted an identical message on Facebook, which did not receive a similar warning.
U.S. states allow voters to still cast a ballot if they were still waiting in line when the polls closed.
In some states, postal ballots that arrive after polling day are accepted so long as they carry a postmark indicating they were mailed by Election Day.