Twitter says it has permanently suspended US President Donald Trump's account due to the risk of further incitement of violence following the storming of the Capitol.
The suspension of Trump's account, which had more than 88 million followers, silences his primary megaphone days before the end of his term.
"After close review of recent Tweets from the @realDonaldTrump account and the context around them we have permanently suspended the account due to the risk of further incitement of violence," the company said in a tweet on Friday.
It was the first time Twitter has banned a head of state, the company confirmed.
Trump has repeatedly used Twitter and other platforms to claim his defeat in the November 3 election was due to widespread voter fraud and to share other conspiracy theories.
He had urged supporters to come to Washington on Wednesday and march on the Capitol to protest the election result.
Facebook said earlier this week it was suspending Trump's account through until at least the end of his presidential term on January 20.
In a blog post on Friday, Twitter said two of the president's tweets posted that day were in violation of its policy against the glorification of violence.
Trump's account had been temporarily blocked on Wednesday following the Capitol Hill siege, and he was warned that additional violations would result in a permanent suspension.
Twitter said Trump's tweet that he would not be attending Biden's inauguration was being received by his supporters as confirmation that the November election was not legitimate.
Another message praising "American Patriots" and saying his supporters "will not be disrespected or treated unfairly in any way, shape or form!!!" could be seen as "further indication that President Trump does not plan to facilitate an orderly transition", Twitter said.
The White House had no immediate direct comment.
The Trump campaign's Twitter account, @TeamTrump, criticised the company for "silencing" the president of the United States.
Twitter also suspended that account.
Using the @POTUS account, Trump said he would look at building his own platform.
Meanwhile Google has suspended the Parler social networking service from its app store, citing posts inciting violence and demanding "robust" content moderation from the app favoured by many Trump supporters.
Apple on Friday gave the service 24 hours to submit a detailed moderation plan.
The actions mean that the network, seen as a haven for people expelled from Twitter, could become unavailable for new downloads on the world's main app stores. It would still be available in mobile browsers.
Right-leaning social media users in the United States have flocked to Parler, messaging app Telegram and hands-off social site Gab, citing the more aggressive policing of political comments on mainstream platforms.
Parler Chief Executive John Matze said in a text message to Reuters, "Coordinating riots, violence and rebellions has no place on social media".
He added in a post on Friday that Apple was applying standards to Parler that it did not apply to itself.
"Apparently they believe Parler is responsible for ALL user generated content on Parler," Matze wrote.
"Therefor (sic) by the same logic, Apple must be responsible for ALL actions taken by their phones.
"Every car bomb, every illegal cell phone conversation, every illegal crime committed on an iPhone, Apple must also be responsible for."