SAN FRANCISCO • US President Donald Trump yesterday threatened to regulate or shut down social media companies, one day after Twitter for the first time added a warning to some of his tweets that told readers to fact-check the Republican's claims.

Mr Trump, without offering any evidence, reiterated his accusations of political bias by such technology platforms, tweeting: "Republicans feel that Social Media Platforms totally silence conservatives voices. We will strongly regulate, or close them down, before we can ever allow this to happen."

He added: "Clean up your act, NOW!!!!"

On Tuesday, Twitter labelled two tweets from President Trump as "unsubstantiated" and accused him of making false claims, a first for the social network which has long resisted calls to censure him over his truth-defying posts.

The move drew a furious response from Mr Trump, who used the platform to accuse Twitter of "interfering in the 2020 Presidential Election".

He added in his tweet on Tuesday: "Twitter is completely stifling FREE SPEECH, and I, as President, will not allow it to happen!"

The social media giant had targeted two tweets the President posted in which he contended without evidence that mail-in voting would lead to fraud and a "Rigged Election".

Under the tweets, Twitter posted a link which read "Get the facts about mail-in ballots" and which took users to a notice calling the claims "unsubstantiated", citing reporting by CNN, the Washington Post and other media.

"Trump falsely claimed that mail-in ballots would lead to a 'Rigged Election'," the notice contended. "However, fact-checkers say there is no evidence that mail-in ballots are linked to voter fraud."

Twitter determined that those unsubstantiated assertions could lead to voter confusion and that they merited a correction, said a person with knowledge of the deliberations who was not authorised to speak publicly.

Twitter, perhaps fearing a clash with one of its most influential users, had previously held out against calls to act over Mr Trump's postings. The tweets in question violated a recently expanded Twitter policy, according to the San Francisco-based company.

In the pair of early morning posts yesterday, the Republican President again blasted mail-in ballots.

Representatives for Twitter and Facebook could not be reached for comment on Mr Trump's tweets. Shares of the companies were down in pre-market trading following his posts.

REUTERS, AGENCE FRANCE-PRESSE, NYTIMES