Twitter has hidden one of President Donald Trump's tweets from his profile, saying it violates rules about glorifying violence.
But instead of being deleted, it has been replaced with a warning and can be viewed by clicking on it.
The warning says "Twitter has determined that it may be in the public's interest for the Tweet to remain accessible."
It is the latest in an escalating row between Twitter and the White House.
Mr Trump was tweeting about the US city of Minneapolis, which has seen consecutive nights of protests following the death of a black man in police custody.
The president said he would "send in the National Guard", and followed that up with a warning that "when the looting starts, the shooting starts."
That second tweet was hidden by Twitter for "glorifying violence".
Twitter's policy of adding a warning to, rather than deleting, tweets that break its rules when it comes to major public figures was announced in mid-2019. But the social network has never used it on Mr Trump – nor deleted any of his tweets before.
"This is the bravest and riskiest thing I've ever seen Twitter – or any social media giant – do," said Carl Miller, from the Centre for the Analysis of Social Media at UK-based think-tank Demos.
"This pours rocket fuel over the online-harm-versus-free-speech debate. Online content policy doesn't get more incendiary than this."
The same post remains unaltered on Facebook, without any warning attached.
For years Twitter resisted calls to treat Donald Trump like any other user and make him follow its rules. Then, on Wednesday, it made a first small move, not removing a tweet but adding a fact-checking link.
The company then had two choices – hunker down and weather the storm or continue to take action in accordance with its stated rules. It has now chosen the latter course of action, calling the President out for glorifying violence.
Any other user would have had their tweet removed, and might have seen their account suspended.
It now looks as though there is no easy way out for either of the two adversaries – a huge battle over the limits of free speech and the rights of social media firms to moderate content is looming.
The move means that other users will not be able to like, reply, or retweet it, Twitter said – but would still be able to retweet with a comment attached.
In a Twitter thread, the social network said: "This tweet violates our policies regarding the glorification of violence based on the historical context of the last line, its connection to violence, and the risk it could inspire similar actions today."
The "historical context" is a reference to the phrase "when the looting starts, the shooting starts" coined by Miami Police Chief Walter Headley in 1967, in reference to his aggressive policing policies in black neighbourhoods.
A later US report found that his "get tough" policy, involving "the frequent display of shotguns and dogs by Miami police in black neighbourhoods" contributed to a state of agitation in the black community until the eruption of the 1968 Miami riot some eight months later.
Twitter said: "We've taken action in the interest of preventing otherRead More – Source
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