Trump Accuses Twitter of 'Interfering' in US Election and 'Stifling Free Speech'

"@Twitter is now interfering in the 2020 Presidential Election," he tweeted after the move targeting his statements on mail-in ballots, adding "Twitter is completely stifling FREE SPEECH, and I, as President, will not allow it to happen!"

Twitter had labelled two of Trump's tweets "unsubstantiated" and accused him of making false claims, a first for the social network which has long resisted calls to censure the US president over truth-defying posts.

The move came amid a growing storm after Trump earlier tweeted a conspiracy theory accusing one of his media critics of murder, prompting an agonized letter from the victim's wife and calls for the company to block the Republican leader's "vicious lie".

Twitter, which has said it is "deeply sorry" for the pain caused by those tweets, has not challenged them, AFP reported.

But it targeted two other tweets the President posted on Tuesday 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 'Rigged Election'," the notice contended.

"However, fact-checkers say there is no evidence that mail-in ballots are linked to voter fraud."

Trump aimed the misleading tweets at California, contending falsely that anyone living in the state would be sent ballots when in fact they will only go to registered voters, according to the notice.

Earlier tweets in which Trump made similar claims did not appear to be similarly labelled.

Trump has long used Twitter as a platform to spread abuse, conspiracy theories, false information and insults to his 80 million followers.

For years before being elected in 2016, Trump built his political brand by supporting the "birther" lie that Barack Obama, America's first black president, was not born in the United States and therefore was not eligible to be president.

And on Tuesday he attempted character assassination of MSNBC host Joe Scarborough by spreading the baseless rumor he murdered an aide.

But Twitter, perhaps fearing a clash with one of its most influential users, had previously held out against calls to act.

The tweets in question violated a recently expanded Twitter policy, according the San Francisco-based company.

"In serving the public conversation, our goal is to make it easy to find credible information on Twitter and to limit the spread of potentially harmful and misleading content," head of site integrity Yoel Roth and global public policy director Nick Pickles said when the change was announced.

Democratic presidential candidate Joe Biden said during a CNN interview on Tuesday that Twitter and other social media platforms should "say it's not true" when misleading statements are broadcast.