Microblogging platform Twitter on Friday flagged tweets calling Democratic presidential nominee Joe Biden “president-elect” and his running mate Kamala Harris “vice president-elect”, saying that official sources may not have called the race.

Vote counting is underway as Biden continues to extend his lead over United States President Donald Trump in Pennsylvania, putting him on track to secure more than the 270 electoral votes to win the elections.

A tweet from Democratic Coalition co-founder and podcaster Scott Dworkin was among the many posts which used either of the titles. “Official sources may not have called the race when this was tweeted,” read a message from Twitter below the tweet. A link to information about the status of the election was attached with the message.

When called out for posting a misleading tweet, Dworkin said it was not so but just an “abundance of caution” from the microblogging platform.

Twitter told AFP that the move was in line with its Civic Integrity Policy and the position it took since the polls closed late Tuesday. Twitter had said that it will label tweets that falsely claim victory ahead of the official results. Those eligible for the label are accounts with 2020 US election tags, US-based accounts with more than 1 lakh followers and tweets that have a significant engagement – over 25,000 responses such as likes or retweets.

“We will label tweets claiming victory that meet our criteria as both Pennsylvania and the presidential race overall have only been called by one source,” a Twitter spokesperson said. “Per our rules, until a second source makes this determination, claims of victory must cite a source that has made the call.”

Twitter had said it would consider results official if state election officials announce it or when it is backed by at least two national news outlets with independent decision desks.

Facebook and Twitter have been scrambling to moderate content related to the US elections, especially those that are misleading or promote violence. On Friday, Facebook banned an online group called “Stop the Steal” that Trump’s supporters were using to organise protests against the counting of votes. Some of the members of the group had called for violence, while many claimed that Democrats were “stealing” the election from Republicans.