Donald Trump says he could start his own social media platform to reach the 88 million followers he can no longer talk to on Twitter.
Many of the president's supporters are moving to other forums less stringent on policing political comments.
After his personal Twitter account was banned, Trump used the official presidential one - @POTUS - to promise them he would be in touch shortly.
He said: "We have been negotiating with various other sites and will have a big announcement soon, while we also look at the possibility of building out our own platform in the near future...STAY TUNED!"
Since Twitter began adding warnings to Trump's tweets claiming election fraud his advisers had been predicting a permanent ban and working on contingency plans.
Twitter said it had reviewed the president's recent tweets "and the context around them - specifically how they are being received and interpreted on and off Twitter".
The social media giant said it had acted "in the context of horrific events this week" and "due to the risk of further incitement of violence".
It cited Trump's tweet on Friday saying his voters would have a "GIANT VOICE long into the future" and saying he would not attend the inauguration.
Twitter said: "These tweets are in violation of the Glorification of Violence Policy. They were highly likely to encourage and inspire people to replicate the criminal acts that took place at the US Capitol on January 6."
It also said that Trump's tweet that he would not be at the inauguration might encourage those considering violence, indicating that it would be a "safe" target as he was not attending.
Twitter also said his use of the term "American Patriots" to describe his supporters was being interpreted as support for the attack on the Capitol, and plans for future armed protests had already begun on the network.
That included "a proposed secondary attack on the US Capitol and state capitol buildings on January 17."
Twitter said: "The two... are likely to inspire others to replicate the violent acts... and there are multiple indicators that they are being received and understood as encouragement to do so."
Jared Holt, who studies domestic terrorism at the Atlantic Council's Digital Forensic Research Lab, said: "They [social media platforms] tiptoed around the issue for years. I guess we found out what the breaking point was, which was insurrection."
Trump has been a member of so-called free speech network Gab since August 2016, and posts the same messages he shares on Facebook and Twitter there. But his recent posts have only gathered an average of 1500 likes.
Gab founder Andrew Torba said it had tens of thousands of signups since Wednesday and had reached 10,000 new members per minute since Trump's announcement. There was anticipation Mr Trump would turn to Parler, a similar outlet billed as a free speech base.
However, Google took Parler off its App Store late on Friday, citing an "ongoing and urgent public safety threat".
Google said: "We're aware of continued posting in the Parler app that seeks to incite ongoing violence in the US."
Apple and Amazon did similar against Parler, meaning Trump now struggles to reach a large audience.
Shortly before it was shut down Trump's @TeamTrump campaign account directed its 2.3 million followers to Parler.
Facebook has suspended Trump until at least Joe Biden's inauguration, while Snapchat has suspended him indefinitely.
Cindy Otis, former CIA officer and disinformation expert, said: "I think he will try to get back on Facebook because of the attention it allows.
"Most people who are on Parler haven't left their mainstream accounts and use them both because they miss 'arguing with liberals' - and there aren't any on Parler."
Trump started using Twitter on May 4, 2009, promoting his upcoming appearance on David Letterman's TV chat show.
Peter Costanzo, who worked for Trump's publisher at the time, pitched Twitter to him as a way of promoting a book he had out.
Costanzo, who made a seven-minute pitch, said: "I said 'Let's call you @realDonaldTrump - you're the real Donald Trump. He thought about it for a minute and said 'I like it. Let's do it."'
Sam Nunberg, a former adviser to Trump, said that in 2011 he would send daily reports on the number of new followers, and Trump would respond "Why not more? Why so slow?".
Nunberg said: "Twitter definitely played a pivotal role in building Donald Trump as a political figure within Republican politics and he also greatly enjoyed it. He used to say 'I wanted to own a newspaper. This is great, it's like a newspaper."'
Trump's most popular tweet was on October 2, 2020 when the president announced he had contracted the coronavirus. It got 1.8 million likes and nearly 400,000 retweets.
Social media strikes back
• Michael Flynn, Donald Trump's former US national security adviser, and Sidney Powell, his ex-lawyer, were banned from Twitter on Friday for promoting the QAnon conspiracy theory, which falsely claims Trump is waging a war against elite Satan-worshipping paedophiles
• Rush Limbaugh, the conservative radio talk show host deactivated his Twitter account soon after Trump was banned. Limbaugh has been on the airwaves for more than three decades.
• YouTube banned the podcast account of Trump's former adviser Steve Bannon on Friday. In November, Twitter banned Bannon's podcast account after he called for the beheading of Dr Anthony Fauci and FBI director Christopher Wray.
• Twitter removed a tweet by Iran's supreme leader Ayatollah Ali Khamenei which suggested that Covid-19 vaccines made in the US and Britain were "untrustworthy".