US president Donald Trump has accused Twitter of interfering in the 2020 Presidential Election after his tweets were flagged with a fact-check warning.

The social media site added a warning phrase to two of Trump's tweets, where he called postal voting 'fraudulent' and predicted that 'mailboxes would be robbed'.

A link reading 'Get the facts about mail-in ballots' has now been added under the tweets, and users are guided to a Twitter Moments page with fact checks and news stories about the claims.

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But Trump says that he, as president, will not allow free speech to be stifled.

He says the social media giant is interfering in this year's election by tagging his tweets.

Until now, the US president has overcome Twitter’s half-hearted attempts to enforce rules intended to promote civility and “healthy” conversation on its most prominent user.

Mr Trump frequently amplifies misinformation, spreads abuse and uses his feed to personally attack private citizens and public figures alike – all forbidden under Twitter’s official rules.

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In a statement, Twitter said Mr Trump’s vote-by-mail tweets “contain potentially misleading information about voting processes and have been labelled to provide additional context around mail-in ballots”.

Meanwhile, the husband of a woman who died in Joe Scarborough’s office two decades ago has demanded Twitter remove Donald Trump’s tweets suggesting the former Republican congressman murdered her.

Twitter issued a statement expressing its regret to the husband but so far has taken no action on those tweets.