World leaders and political figures who use Twitter to threaten or abuse others could find their tweets slapped with warning labels.
The new policy, announced by the company on Thursday, comes after complaints from activists and others that President Donald Trump has a free pass from Twitter to post hateful messages and attack his enemies in ways they say could lead to violence.
From now, a tweet that claims to involve matters of public interest but breaches the service's rules will be obscured by a warning.
Users will have to tap through the warning to see the underlying message but the tweet will not be removed, as Twitter might do with a regular person's posts.
The company said the policy applied to all government officials, candidates and similar public figures with more than 100,000 followers. Twitter will also not elevate or promote such tweets.
"It's a step in the right direction," said Keegan Hankes, research analyst for the Southern Poverty Law Centre's Intelligence Project, who focuses on far-right extremist propaganda.
But Mr Hankes said that Twitter was essentially arguing "that hate speech can be in the public interest. I am arguing that hate speech is never in the public interest".
Twitter would not say whether any of Mr Trump's tweets had breached its rules, or whether his posts played any part in the new warning-label policy.
The new stance could add to the US president's anger against social media. He often complains that social media sites are biased against him and other conservatives.
Twitter's rules ban threats of violence against a person or group, engaging in "targeted harassment of someone", or inciting others to do so.
It also bans hate speech against a group based on race, ethnicity, gender or other categories.
Up to now, the company has exempted prominent leaders from many of those rules, saying that controversial tweets from politicians helps to hold them accountable and encourages discussion.
But there have been calls to remove Mr Trump from the service for abusive and threatening behaviour.
Activists have complained this week after he threatened Iran with "obliteration" in some areas if it attacked the US.
Mr Trump has also tweeted a video of himself beating up a man with a CNN logo in place of his head and retweeted anti-Muslim videos.
"Donald Trump has changed political discourse on Twitter and everywhere else, given the level of toxic statements he has made about vulnerable communities in America," Mr Hankes said.
Other politicians could become subject to warning labels.
In 2018, French prosecutors filed preliminary charges against far-right French politician Marine Le Pen for tweeting brutal images of ISIS violence. Twitter prohibits material that is "excessively gory".
And in March, Brazilian President Jair Bolsonaro stirred outrage by sharing a video on Twitter of a man urinating on the head of another man during a Carnival party.
Insults and mockery fall into a grey area. Calling someone a "low-life", a "dog" or a "stone cold loser", as Mr Trump has done, may not be a breach. But repeated insults against someone might amount to prohibited harassment.
Jennifer Grygiel, a social media expert and professor at Syracuse University, said Twitter enacted the new policy because of Mr Trump's Twitter activity.
But Prof Grygiel said the new rule did not go far enough.
Because of his ability to start wars, move stock markets or influence world events, Twitter should review leaders' tweets before they are sent out and block them if necessary, she said.
Twitter's new policy does not apply to past tweets.
Twitter said it was still possible for a government official or other figure to tweet something so egregious that it warranted removal. A direct threat of violence against a person, for instance, would qualify.
The company said warning-label decisions would be made by a group that included members of its trust and safety, legal and public policy teams, and employees in the regions from where the tweets originated.
