US President Donald Trump has been permanently suspended from Twitter "due to the risk of further incitement of violence", the company says.
Twitter said the decision was made "after close review of recent Tweets from the @realDonaldTrump account".
It comes in the midst of the online outlets used by Trump and his followers being purged by Big Tech.
Some politicians and celebrities have been calling on Twitter for years to absolutely ban Trump.
Former First Lady Michelle Obama tweeted on Thursday that the Silicon Valley giants should stop encouraging and permanently expel Trump's "monstrous behaviour"
Reacting to the ban on the president, Trump 2020 campaign adviser Jason Miller tweeted: "Disgusting... if you don't think they're coming for you next, you're wrong."
Why was Trump banned?
On Wednesday, after he called the people who stormed the US Capitol "patriots" Trump was locked out of his account for 12 hours.
As the US Congress attempted to certify Joe Biden's win in the presidential election, hundreds of his supporters stormed the Capitol building. The violence that followed resulted in the deaths of four people and a police officer.
Twitter warned then that it would ban Trump "permanently" if he breached the platform's rules again.
After being allowed back on Twitter, Trump posted two tweets on Friday that the company cited as the finals straws.
In one, he wrote: "The 75,000,000 great American Patriots who voted for me, AMERICA FIRST, and MAKE AMERICA GREAT AGAIN, will have a GIANT VOICE long into the future. They will not be disrespected or treated unfairly in any way, shape or form!!!"
Twitter said this tweet "is being interpreted as further indication that President Trump does not plan to facilitate an 'orderly transition'".
In the next, the president tweeted: "To all of those who have asked, I will not be going to the Inauguration on January 20th."
Twitter said this was "being received by a number of his supporters as further confirmation that the election was not legitimate".
Twitter said both of these tweets were "in violation of the Glorification of Violence Policy".
After Twitter had permanently suspended his @realDonaldTrump account, Trump tweeted from the US president's official @Potus account suggesting he would "look at the possibilities of building out our own platform in the future" and railing against Twitter.
But the tweets were removed from the platform as soon as they were posted.
Are other tech firms blocking Trump or his supporters?
Earlier on Friday, the company permanently banned two Trump loyalists: former national security adviser Michael Flynn and attorney Sidney Powell.
Later in the day, Google suspended Parler - a self-styled "free speech" rival to Twitter that is increasingly popular with Trump supporters - from its online store.
"We're aware of continued posting in the Parler app that seeks to incite ongoing violence in the US," said Google.
On Thursday, Facebook said it had suspended Trump "indefinitely". The popular gaming platform Twitch also placed an indefinite ban on the outgoing president's channel, which he has used for rally broadcasts. So has Snapchat.
Two online Trump memorabilia stores were closed this week by e-commerce company Shopify. On Friday, Reddit banned its "donaldtrump" forum for the president's supporters.
Why was Twitter such a potent tool for Trump?
Trump used Twitter to taunt critics, cheer supporters, fire officials, refute "fake news" and vent complaints, mostly to highlight his point by using all capital letters and exclamation points.
The media allowed him to circumvent mainstream media and link instantly with almost 89 million followers, while critics said the posts were a flood of misinformation.
His tweets were also known for the occasional spelling error, and he sometimes left followers guessing with apparent mis-types, such as when he posted, "Despite the constant negative press covfefe".
The Department of Justice said in 2017 that Trump's tweets were "official statements of the President of the United States".
What else did Twitter say?
Twitter wrote in a blog post on Friday: "In the context of horrific events this week, we made it clear on Wednesday that additional violations of the Twitter Rules would potentially result in this very course of action.
"Our public interest framework exists to enable the public to hear from elected officials and world leaders directly. It is built on a principle that the people have a right to hold power to account in the open."
It added: "However, we made it clear going back years that these accounts are not above our rules and cannot use Twitter to incite violence. We will continue to be transparent around our policies and their enforcement."
Some 350 Twitter employees had signed a letter this week to the company chief executive, Jack Dorsey, asking him to ban the president in the wake of the Capitol riot.
The letter said: "Despite our efforts to serve the public conversation, as Trump's megaphone, we helped fuel the deadly events of January 6th."
When did Twitter first take action against Trump?
Twitter first took action against Trump in May 2020 appending fact-checks to tweets he sent claiming postal votes were fraudulent.
Later that same week it posted a warning label when the president threatened to send in the military to quell Black Lives Matter protests as he added, "when the looting, starts the shooting starts".
Twitter used these fact-checks and warning labels increasingly throughout the year for Trump tweets about coronavirus and the presidential election.