Twitter has marked a post by Donald Trump as "misleading" after the President said "surprise ballot dumps" were aiding rival Joe Biden.
It follows two posts that were censored late into election night, in which Mr Trump had claimed rules that allow postal ballots to arrive at voting centres after polls closed amounted to election theft, and claimed to have secured “a big win” in Tuesday's vote.
“We are up BIG, but they are trying to STEAL the Election. We will never let them do it. Votes cannot be cast after the Polls are closed!” one post said. The other added: “I will be making a statement tonight. A big WIN!”
The two posts came shortly after Joe Biden had appeared in front of supporters and claimed to be confident about the results, and appeared to be an effort by Trump to regain the initiative as the election remains too close to call with large numbers of votes still being counted in crucial states.
We are up BIG, but they are trying to STEAL the Election. We will never let them do it. Votes cannot be cast after the Polls are closed!
— Donald J. Trump (@realDonaldTrump) November 4, 2020
Within minutes, the first post was restricted by Twitter, which hid it behind a warning label declaring it may be misleading about how voting works, and prevented users from retweeting the post to their own followers or liking the tweet.
A spokesperson said: “We placed a warning on this tweet for making a potentially misleading claim about an election. This action is in line with our Civic Integrity Policy, and as is standard with this warning, we will significantly restrict engagements on this tweet."
Facebook then added its own label to the same post on its website. It took similar action on Mr Trump’s second post declaring he had secured “a big win”.
While Facebook labelled both posts, adding clarifications that election results are not final, Twitter did not take action on Mr Trump’s tweet claiming to have won.
"As of now we have not placed a warning on this tweet as the language is vague and unclear about what victory is being claimed," the spokesperson said.
Facebook later said it had also "started running notifications on Facebook and Instagram that votes are still being counted and a winner is not projected".
However, this is not thought to apply to individual states, and instead only to the overall result of the presidential race. Facebook told The Wall Street Journal on Wednesday it would be allowing candidates or supporters to say they had won in battleground states even if the outcome in those states remained in dispute.
It said the move was "to address premature calls for the final result of the presidential race".
"For other posts we are applying labels directing people to them in the Voting Information Center where they can see what races have been called.”
It has also applied labels to posts by Democrat and Republican officials in the battleground states of Wisconsin and Florida, warning users that the information may be contested or inaccurate.
Still, the moves by Twitter and Facebook are likely to provoke an outcry from the Trump camp, which has often accused social media companies of attempting to censor him. Both companies had previously stated they would be taking action against candidates who declared premature victory in the run up to the election.